Hey guys, looking at this gear from ryda and wondering if it will all work together and sound good.

http://www.ryda.com.au/Pioneer-TS-C1602-Ca...s-p/tsc1602.htm
Those splits powered by this amp
http://www.ryda.com.au/Clarion-APX2121-2-C...r-p/apx2121.htm

And finally this Sub/amp combo
http://www.ryda.com.au/Clarion-SP12XBA-12-...p-p/sp12xba.htm

Thanks guys, probs a stupid question but I'm new to the car audio game.

Sound is dependant on a shitload more things than just speakers and amp. I am personally not a fan of Clarion gear at all, nor the setup you've got going. Much better would be the Pioneer splits, a Jaycar (or other cheap/decent) 4 channel amp and a single 12" boxed woofer.

If I get the 4 channel I can run the splits and the sub off it aye?

Yes, you can just bridge the rear channel for the sub.