Using both speaker-level / RCA outs

My nephew has a Pioneer head with 1 rear channel RCA out. He’s got a 4 CH amp pushing the rear CH, and bridged the remaining 2 for a sub.

Now he wants an amp to power the fronts. So he doesn’t lose fader control, he’s going for a speaker-level input to the amp.

Don’t you use either high or low level outs, no matter what(?).

Question: Can you both use the head unit’s low-level RCA for the rear and speaker-level for the front?

Use a line level output converter on the radios front channels to feed the amp. Make sure it can handle the power the radio is putting out. That would be your safest way of getting a signal.

Thanks, guys.

Let me reiterate… My car’s Blau has 2 sets of preamp line outs (so using speaker level outs/ins is out of the question). From the O-Manual, it summarily states using either line or speaker level out to amps. Or, you should not use (say) the front CH speaker level for a 1rst front amp, and simultaneously use the rear CH line out for a 2nd rear amp. Frankly, I don’t see why not.

So, in my nephew’s case, he’ll be using the head speaker level out for the front CH 1rst amp. And, the rear CH RCA line out for the 2nd amp. Question being: Is this ok?