Or so we thought. A subsequent drive on demanding UK roads (070), in the company of its fiercest rivals - Bentley Continental GT, Porsche 996 Turbo and Mercedes SL55 AMG - gave the DB9 a more complete interrogation. The result was an unexpectedly bloody nose for our new British hero, beaten by the 911 and SL, and roughed-up by the Bentley as well. We concluded at the time: 'There's a great car locked inside the DB9. On paper it's a winner, but the driving experience simply doesn't reflect this, which is immensely frustrating.'

Almost two years on from that disappointing day, we're driving another DB9, this time fitted with a new 'Sports Pack'. Comprising a number of changes, it amounts to a thorough reworking of the DB9's chassis and will hopefully address those dynamic shortcomings that made the DB9 such a bittersweet experience.

The first and most obvious change is the wheels. Retaining the original car's 19in diameter (and Bridgestone tyres), the new rims are forged aluminium in a simple but striking five-spoke design. Together with titanium wheelnuts, they shave more than 1kg of unsprung weight from each corner, reducing the dampers' workload on bumpy roads and aiding the car's composure.

If you've got a real eye for detail you may also be able to spot the reduction in ride height, by a modest 6mm. While that's as far as the visual changes go, there are plenty more hidden from view. The spring rates have been upped significantly, with a 68 per cent increase at the front and 64 per cent at the rear. The front anti-roll bar has also been changed and the dampers revised accordingly to make the most of the changes.

Finally, and perhaps most intriguingly, the standard car's composite undertray has been replaced by a load-bearing aluminium panel. In addition to performing the same function of managing the DB9's underbody airflow, this new panel increases the car's structural stiffness, allowing the suspension to work without distraction and, in theory at least, improving the chassis' response on turn-in.

To put all these changes to the test, we've headed to South Wales and the roads that uncoil across Black Mountain. Not only will these tricky hill-roads test the DB9's sporting credentials, but the long hours of motorway driving to get there will establish whether its long-distance GT qualities (already tested by the standard car's surprisingly hard-edged character) are preserved, enhanced or compromised by the more focused Sports Pack set-up.

There are some things at which the DB9 has always excelled. Things like delivering an unrivalled sense of well-being from the moment you clap eyes on it. Those fluid curves are as mesmerising as ever, and once you press the flush-fit door handle, pull gently on the thin, protruding finger and swing open the 'swan wing' door, you feel yourself falling for the DB9 all over again.

Twist the key, dip the clutch, then pause to savour the soft red glow of the glass starter button before finally pressing it to awaken the 6-litre, 450bhp V12. The Sports Pack doesn't meddle with the engine or exhaust, but it doesn't matter, for the DB9 has always cleared its throat with a rousing snort. As the revs flare then fade to a meaty burble at idle, the process of seduction is complete.

It's hard to know what to expect from an upgrade like the Sports Pack, but such an immediately obvious transformation is a big surprise. The DB9's steering was one of the main areas of criticism in that fateful group test, but almost from the off this car feels lighter and keener, with none of the sticky, stodgy, over-weighted feel of the standard car. Aston claims not to have changed the steering itself, but you'd swear it has been completely re-engineered, such is the improvement in feel.

The brakes of the standard car shared the steering's slightly treacly feel and lack of sensitivity, but they too feel more progressive on this car. Perhaps it's a result of some ongoing development. It's certainly hard to believe that the lighter wheels - and therefore reduced flywheel effect - could bring such an improvement. No matter, for whatever the source, it's a welcome advance.

On the long drive to Wales the ride shows no signs of gaining any sharp edges. In fact if anything it feels more supple, absorbing bumps and ridges - especially single-wheel movements - with more composure and sending less of a shock through the all-aluminium structure. There's still the occasional shimmy through the steering column, but it's rare, and less noticeable than in the standard car. The bracing effect of that new aluminium panel perhaps?

The fast, twisting and generally bumpy roads that lead to Black Mountain come as a welcome relief after the endless monotony of the M4. The DB9 feels deliciously grunty, that big-lunged V12 pulling impeccably from little more than tickover and displaying a real enthusiasm for revs. After its relaxed, loping gate on the motorway, this spirited pace and appetite for real roads is the hallmark of a great drivers' GT.

It's on roads similar to this that the standard car proved compromised, lacking the lightness of touch, not to mention the wheel travel, to find a rhythm with the road. The Sports Pack-equipped car tackles the road with more enthusiasm, turning in more incisively and with less effort thanks to the lighter, more delicate steering. You can also make mid-corner corrections more easily, too, which makes the DB9 feel more intuitive to drive quickly.

There are still occasions when the chassis seems to lack wheel travel - despite the Sports Pack's modified bump-stops - at which point it momentarily loses the suppleness and tiptoe feel it has worked so hard to cultivate. These moments are rare, though, and do little to detract from the increased high-speed poise and the overall uplift in dynamism that cements the illusion that the DB9 has miraculously shed a hundred kilos.

While the Sports Pack enables the DB9 to dispatch high-speed corners with an abundance of grip and newfound enthusiasm, tight corners still test its ability to find traction. With the ASR system engaged you can feel the electronics and V12 indulging in a bit of arm-wrestling, while switching the system off is only recommended through clearly sighted corners, for given free-rein the DB9 can get surprisingly hairy surprisingly quickly. While fun, it soon becomes clear (once the smoke has dispersed, at any rate) that the DB9's preferred style is neat and tidy, not fast and loose.

At what amounts to pin money for the average Aston owner, it's hard to imagine anyone not ticking the Sports Pack option box. Not only does it transform the steering feel and response, but the increased bite and poise makes the DB9 a much more convincing drivers' car, and all without compromising its role as a smooth, refined mile-eating GT. In fact, if anything, the changes make it more cosseting than the standard car.

The Sports Pack goes on sale both as an option on new car orders and, encouragingly, as a dealer-fit upgrade for the DB9s that are already out there. While that's great news, our experiences suggest that rather than satisfying a niche demand, Aston Martin would be wise to incorporate the Sports Pack's changes into the standard car, for they are the key to unlocking the DB9's greatness.