oh, 5 year old shift cables? for sure, spend the $5 or whatever on two new decent quality shifter cables and do that before you start upgrading.
I wouldn't use a 10 speed chain on a 8 speed triple-crank, the chain could drop between sprockets and jam. a 9 speed chain isn't hardly narrower than the 8, so it would probably work OK.
I really wouldn't use any 10 speed parts on a 8 speed rig. Also, I would stick with MOUNTAIN parts, not road, as the Sirrus frame has a mountain bikes rear end spacing.
if I was stupid rich and just blinging it for the heck of it, I'd consider going 3x9 with a complete makeover, using Deore LX 'trekking' stuff, 48-36-26 front crankset and suitable 9 speed mountain shifters, derailleurs, and of course a 9 speed cassette and chain. While i was at it, I'd probably be upgrading the wheels, some nice Handspun wheels with deore hubs and suitable rims, etc. but that all is more than your Sirrus is worth. (my bike, pictured in closeup above, is a Specialized Globe Vienna, which is basically a 2010 Sirrus base model with different paint).