I want to add midbass to my system. What is the best way to filter the signal so these speakers only play midbass? I am getting Some ID 6.5"s to add to the rear for midbass. I want to run them in mono to preserve the soundstage up front where I have separates. I am about to order an Eclipse PA5422. I want to run the front 2 channels with two component speakers in stereo at 2 or 4 ohms (any ideas on some good 3 way components for this setup?) but I want to bridge the rear 2 channels for the midbass with two 4 ohm speakers in parallel to produce a total 2 ohm load at the amp. Is it possible to do this setup (one set of channels bridged other two channels running standard 4 or 2 ohm load? Am I correct in using 4 ohm speakers for the rear in parallel for this setup?
Lastly, most component speakers (for front) run at 4ohms right? Or is there big selection of 2 ohm varieties?
As for question one: I do have a crossover built into my Pioneer Premier DEH-860 HU but should I add a passive filter to cut out the highs to have my ID 6.5s play midbass or is there a better way to crossover for my application?
I want to bridge two of the channels for the midbass (or any other configuration to make the rear midbass play in mono) and use the front two channels in stereo (a speaker hooked up to each of the remaining two channels)
Okay, your setup is reasonable, but not really recommended. It depends on the power loads for each of those midbass speakers. If they are ~100W RMS, you should be OK.
Personally, I would get a Phoenix Gold crossover to convert the incoming signal to mono before the amp and adjust the midbass on it as needed, but that's another $150 you probably don't want to spend.
Up to you and your budget, although adding another mono amp would cost about the same thing and be a bit more predictable.
Since you're only interested in creating a "more filling" experience, then that amp probably isn't for you. The rear crossover is clipped at 120Hz, which, while officially "midbass", is going to be more of what I would call "weak low bass" than anything else. There are plenty of other amps (Kenwood 8401, for example) that let you set a low-pass at 200Hz, which is the target you're looking for (150-200Hz).
The stereo vs. mono argument isn't very significant for midbass. Mono is better for full subwoofers amps (Class D) because it requires less processing/power (hence, heat and distortion) for the same amount of wattage. You're not driving 12" subs, so it's of little importance in this case.
Many subs are available at 2 ohms (less impedance=more power), and there are applications where you would bridge two 4-ohm subs to 2-ohms on a channel, but this isn't one of 'em.