Hi PRA, welcome to the madhouse ..... If you are keen to keep the bike standard then you'll need to pick up a set of down pipes,( both the same ).. and a pair of collar clamps, and 4 new nuts, and check the studs in the head are good... often they aren't, so you may be involved in a bit of work removing and replacing studs. that silencer on ebay (in Ians post) is as good as it gets for standard gear these days..
OR... get a bespoke job.. not cheap... but at least you can decide exactly how you want it to look.... plenty of pics in the gallery here.
I tend to use standard down pipes and get a silencer made up to marry on to them. Going this route you can use the siamesed down pipes from the monoshock SRX (400 & 600 are the same, as are the 400 & 600 twinshock)... using the siamesed pipes makes fabrication of the silencer a trifle easier.. good luck with the bike... post some pics when you have time.
