small wiring dilemma

The vehicle is a 2002 Silverado.  I have two amps one 4 channel the other a 2 channel. Neither will accept high level inputs. I am keeping the factory head unit. I have purchased the Ven 4 which is a 4 channel output converter however, I need 5 channels. The 4 channel amp is going to run the 4 main speakers and the 2 channel will be bridged to run the subwoofer. I just got to thinking how am I going to get all 5 channels? The converter has two sets of RCA outputs but the 4 channel amp will need both of those. The options I can think of are,

1. Use the head units power for the two rear speakers which Id rather not do. I already have the wiring run from the amps to the speakers plus I want the amps power to all speakers.

2. Use Y adaptors on the 4 channel so the 4 channel RCA input will be filled with just one cable. I have never used these so I dont know if this will hurt performance or not?  Will it even work?

3. Bridge the 4 channel amp and hook all 4 speakers to just the two channel setting. Im thinking Im going to lose my fader control either way because the outputs from the head will be split to the sub and speakers since I have added an extra speaker. The four speakers I have installed are quality speakers so power handling shouldnt be much concern.

Can you guys think of any other options?  If not what do you think is the best way to go?   Thanks Boomer

No unfortunately there is no RCA out on the amps. That daisy chain feature would be nice here.

Dyohn thanks that sounds simple enough. I guess your saying connect it right at the output of the VEN 4?

Sounds good, anyone object?

Thanks Dyohn and Forbidden.