As far as amps go, stock MP#, yes? I'm pretty sure those came with a bazooka of sorts, I'm sure 1sty will know. At anyrate, as for stock speakers, I believe the wattage rating would be around 60wrms, thatsaid, ANYTHING will work, and with much more than even 30, you'll likely be out-playing your subs capabilities. ALso, look into that pg o5.1 amp, it'll push everything AND has sub output as well, all in one easy package, thisway you could get true surround if you've got, or can manage a digital output.
sirius-wise, I know that while it seemed easy and everyone seeemd to say it was a no-problem kinda thing, actually connecting XM to my carputer was a PITA... I wound up just sorta stumbling around, trying diff settings, and eventually finally running the audiot input part of it directly to the mobo.