Well do tell

the easiest way is to pick one groupset, ie shimano xt or SRAM x7 and use that for the entire drivetrain, i prefer to have x9/x0 shifter derailleur, SRAM cassette and KMC chains, its all personal preference

RANDOM THOUGHT:
What's wrong with your 8 speed setup?
If it were me, I'd just be replacing the 8 speed (with 8 speed). You can still get XT 8 speed cassettes which are as good as anything else on the market, if that's too spensy go with a deore.
8 speed is bulletproof

Bloody good point, Conners!

It doesn't happen often, but sometimes - just sometimes, I can chime in with something useful...

Conners wrote:If it were me, I'd just be replacing the 8 speed (with 8 speed).

Sram PG-850 cassette and chain, cheap and perfectly functional, and the sram chain comes with the nifty powerlink in case you can be bothered taking it off to clean it.

8spd for the win!!! 850 cassette and a hg50 chain bol. lasts heaps longer than 9 spd