Hey guys i only have 2 sets of RCA outs from my head unit, is it possible to hook up a 4 channel amp as well as a mono block amp and have all the speakers (Front L&R, Rear L&R, Sub) being powered off the amp? At the moment i only have RCA's going to the mono block amp which is obviously powering the sub.

Also how do i connect a 2 amp system up? I can only seem to get one amp to work at a time.

At least one of the amps should have an input and output rca sockets..
If the mono has the rca outputs run the Rear rca cables to the inputs of the monoblock and then get another set and connect them from the monoblock rca outputs to the rear input of the 4ch, fronts just go straight to the 4ch like usual..

And vice versa if the 4ch has the outputs, Rear outputs to monoblock inputs..

Not sure if its the best for sound quality but it'll get it all going at least..

Was hoping Stone would answer this lol.
Honestly I wouldnt amp your rears, theres no real point. Would solve a big problem as well, but if you insist on amping them:
If you dont have an RCA through on your 4ch amp, then you'll need to split the RCAs (using a 1-2 splitter) on the rear channel.

To get power to both amps:
You'll need a distro block. Eg 4g into a 2outlet distro, then 2x8g out to the amps (or 1x8g and 1x4g).
Then you need to piggyback the remote wire from one amp to the other so they both turn on.
Doing this means that you wont be able to switch the sub on or off or even adjust it from the headunit. You could run another remote wire from the headunit with a switch and that would solve that.

If you dont amp your rears, and use those RCAs for the mono then its possible that your headunit can switch them on or off.