Why Cant I Do this

I have 2 300rms subs (4ohm)
I hook 1 amp that is 300rms (Bridged 4ohm) to 1 sub and it works fine.
Then b/c i have 1 pre-out on my deck i use the out-put on the amp to hook up my other amp. The other amp is 200rms (Bridged 4ohm). When i play it works great for 2 minutes then my entire systems sound gets cut in half. (half the sound at the same volume). Why cant i hook up 2 amp to my 1 output deck, and i'm not sure waht to do.

Should I: (the best cheapest way for my system to work properly)
1. Just get an amp at 600rms at 2ohms and hook up both subs to it.
2. Split the rca cable with 2 y's to create 2 rca cables to goto the amps.
3. Get a newer Deck.
4. The amps aren't getting enough power. (need bigger gauge wires)
5. Other way please tell

TY

when it gets half as loud, are either of the amps off or in protection?

Theres still bass from the subs so they'd have to be on.

Well, can't really say without looking at it. Personally, I'd either take one amp and run it 4ohm stereo or get a better amp that can go 2ohm mono.

The amps work fine by themselves to 1 or 2 subs, and there both 1 ohm stable. but when i hook both amps up they dont work.

incase your confused i have 2 subs and 2 different amps, i hook 1 amp to 1 sub and the other amp to the other sub, but due to 1 output on my DecK i have to run the rca cables input on one amp and output that and input the other. That's when it doesn't work. (you know you have an input and an output on your amp).