if you bridge the X100.2, you'll only end up with 1 channel. that obviously won't work with a set of L+R splits; you'll need 2 amps. hardly economical.
overall, the X100.2 is a superior amp to the SRx2, in both power, build quality, and performance (this last point is based upon my perception rather than actual use of an X100.2). i use a couple SRx2 amps for minor duties - ambient tweeters and centre channel - and they're a good compact little amp with great performance at this pricepoint. only 'downers' are the fiddlly controls and screw-holes, but these are set-and-forget so easily dismissed as being major probs. build quality is fine if not plasticky and not a patch on a xenon.
there's no rationale to matching brands/series of products, so the xenon amps are not specifically matched to xenon splits.
stock HUs tend not to have RCA preouts. instead you have to rely on the speakerwire outputs. this is a bit inferior because the signal passes through the internal amps first, and these are usually 'average' at best, so degrade the signal very slightly. it would be a pity to use a factory HU and a high quality amp like the xenon. will you change the HU later?
anyway, relying on the speakerwire outputs means you need an amp with speakerwire (high-level) audio inputs or use a separate converter (line-output converter aka line level converter, etc). the SRx2 features high level inputs whereas the xenon does not. a separate quality LOC will be $80+ or so, or check out the navone model:
http://www.caraudioaustralia.com/forums/in...57673&hl=navoneit's a bit of an 'unknown' as to the quality of the LOC inbuilt into many amps, the SRx series included, but i would expect it to be fine.
aside from any ebay issues, i'd go the X100.2.