amp problems

[Lee SRi]

i have 3 amps, and the headunit i have only has 1 lot of rca's.
i have got a double connector for it, so basically i have 2 lots of rca's. how do i go about the 3rd amp without buying a new stereo?

also my amps arent working?
i bought an amp from someone my mate knows, came to wire it up and the power keeps turning on then straight back off. i bought a big power wire and a new fuse holder, big earth, checked the fuses.. still no joy.
and my other amps power is turning on, but theres no sound going through my speakers??

ive spent 2 days trying to solve the problem, cant think of what it is. so was gonna get an auto electrician to do it but if someone knows the problem im having though id prefer to do it myself.

1 amp is a 600w 4/3/2ch predator amp
1 amp is a 300w 4ch splx amp
1 amp is from an splx bass tube (taken apart)

the problems not with the bass tube amp (only the fact ive ran outa rca's)
its the other 2 amps, the splx amp i used for about 3mnth without any problems. i tested the predator amp in my car using the wiring from the splx amp, and it works fine.
now neither of the amps are working? and i doubt both amps have blown.

if anyone could help me with any of my probs it would be appreciated.

thanks