I have a DLS ca31 3 channel amp.
its ratings are

2x75wrms 4ohm
1x170rms 4ohm

i currently have a 12" diamond sub and diamond components hooked upto this amp.

on the mono channel for the sub it is possibel to connect 2 subwoofers to it in parralel, like +-+-. the door components are hooked upto the other 2 channels.
so the channel with 1x170rms is hooked upto a diamond 12" sub and has space for another subwoofer.

my question is what rms rating would the new sub need be to make sure no clipping of sound etc. i mean does teh 1x170rms half when 2 subs are connected or does the channel kick out 170wrms through both the channel conections.

basically guys if theres 2 connectors on one channel on an amplifier. which has a rating of 1x170w, whjat rms rating must the subs be that i would connect to the channel. i.e would i need 2 subs at 170rms or 85 rms each

That 1 x 170 jumps to 1 x 280 @ 2 ohms, connect 2 4 ohm subs to it and that's what you'll get, but that means only 140 to each sub. What are the subs rated power handling rms? You might be better of buying one dual 4 ohm voice sub to get the most out of the amps mono channel, you don't want to under power your subs.