Plenty of cars running rear engines and quiet exhausts with good hp levels and without the associated problems vx owners seem to have so cant believe its not possible, just cost prohibitive to develop i guess.
Actually.. Quite a few modern fast cars like Fezza's, AM's and fast Porkers get kicked off of trackdays with their OEM exhaust systems.
Especially the 'flappy' ones tend to do fine on a static dB test, but on track they get way too noisy when the flaps open up under load.
And you can't keep the flaps closed as they will overheat the exhaust system with them shut.
Still... Some tradeoffs/compromises have to be made when it comes to dB reduction versus physical space and exhaust flow.
You can't expect to run virtually 'open pipes' with just small absorption silencers on 300Bhp cars and then remain under stricter (eg. 80dB) driveby levels unless you fit a few massive silencers and for instance sacrifice the boot in the cars to obtain that goal. (something more 'race' oriented cars tend to do.. and indeed it works!)
Also do not underestimate the amount of noise a lightweight single-skinned silencer will (re)transmit to the outside simply by resonating the outer surface/skin. (also a major source of any 'drone' in a car..)
To get high dB attenuation in a small silencer package you need to start going to chambered silencer designs like the OEM silencers are and do a double-skinned setup or ar least thicker walled silencers with ridges/creases folded in the skin to get it out of the resonance frequencies.
Will this be heavier? Yes, likely.. Will it perhaps not flow as well as a straight absorption silencer: Also likely.
But will it pass the noise limits and not pose a risk to the engine like many of the 'add on' dB killer 'plugs': yes, definitely.
Does it need to be expensive? No.. An adventurous VX owner could try start looking at building a system with generic chambered silencers for lorries and HGV's. These are pretty much starting at 3" and are meant to package a lot of silencing in small(er) spaces.
Will it look 'sexy'? No... Will it work: quite possibly.. Worth some experimentation I'd say..
Also a lot of lorry/HGV stuff for intake and exhaust parts has *actual* data on air flow capacities, pressure drops and dB reductions unlike most of the 'chooner' stuff that always promises a lot, but often end up kinda 'meh'..
Also dig around for possible OEM silencers from other 'big engine' or 'big horsepower' cars on the road and see which could be made to fit the exhaust area on a VX and then start digging around on some scrapyards and experiment! 
Bye, Arno.
It really is nice without the SC whine.. 
