I'm wondering if it's ok to feed into both front and rear Hi level inputs on a Sony xplod XM-554ZR from one source (my rear speaker out of factory head unit).

I can't imagine the head unit would care - no different than paralleling speakers.... and the Hi In of an amp wouldn't be low impedance would it?
My factory speakers are 4 ohm so the head unit is ok with that Imp.

overview:
I just want a bit of bass boost for my factory system.
It will be fed from the existing speaker leads into the High lvl inputs.
Then back out to the factory 6X8's from the "front" outputs.
Then, I am bridging the rear output to drive a single 10" bandpass sub.
I'll just use the gain controls on the amp to balance the bass.
Everything hidden in the trunk, and passive is what I'm after.

thanks!

?

anyways - it worked. I just biased the pots to balance the volumes.
Both low pass (rear) and high pass (front) filters ON
Bridged rear to sub -gain pot at 7/8
stereo out "fronts" to rear deck spkrs -pot at 1/3
gobs of bass and maintained stereo separation on the low end. Exactly what i wanted.