LOC neccessary?

my HU has got dual preouts (front/rear  or front/subs). I'm thinking of hooking up the front and rear channels to an amp, and have a separate amp for a sub, so i want to keep the sub rca-outs free and the only way I can get my rear speakers to RCA level is by using a LOC. is there anyway i could avoid having to do this? As i've heard that LOCs may cause your SQ to decrease. If theres a way to minimalize this as much as possible, how do i go forth about it?

Thanks

well.. the thing is that the rear or sub pre-outs can only be used for either one as you can set it on the headunit if you want it as sub woofer output or not and i'm afraid if i connect the sub and the rear 6x9 on the same channel, it might drain the treble on the 6x9.

p/s i'm here on my computer and at the same time crimping the terminals on my wiring harness, was wondering if theres a difference between Illumination & Dimmer. Do they go thru the same +12V each time the lights are on? or are they the opposite of each other?