I think the C5 RS6 wheels look a little 'heavy' on the S4 - too much metal going on, if you know what I mean? I like the look of the B7 RS4 wheels but could be tempted by the C6 spoked wheels as well. Depends on what sizes are available and how silly it ends up looking if they over-wheel the arches without ridiculous profile tyres.
As for the rest, I doubt the LPG install can be done by anyone other than an approved installer, so they're unlikely to do a proper remap for engine management as well. Might be worth talking to Viper on SRS forum as he seems to have a good rep for oddball requests like this. Most places will flog you a Milltek at RRP but they do crop up used on ebay so worth keeping a look out as they're mental money new. Worth a browse of the catalogue on the Milltek site as they list all the part numbers and on the B6 you can generally find a system and maybe change one section for a new part. With yours being manual you could go non-resonated if you wanted to be more antisocial on the noise front 
__________________
===SOLD===2002 Audi S8 D2 Final Edition (yes, really) in Avus Silver with purple extended leather===SOLD===
2011 S5 Sportback in Phantom Black with black Super Sports leather, 9x20s, tech pack high, adaptive xenon plus, intelligent key, memory seats pack, sunroof, B&O, Audi Drive Select & quattro Sports Diff, DAB, parking system plus
2015 VW Golf GTI Performance Pack in Carbon Grey with black Vienna leather, tech pack (Discovery Pro nav & Dynaudio), DCC, factory towbar and retrofit RVC
|