Hey I have a blaupunkt THA475 amp. Specs:
4-channel car amplifier
75 watts RMS x 4 at 4 ohms (120 watts RMS x 4 at 2 ohms)
200 watts RMS x 2 in bridged mode (4-ohm stable in bridged mode)
variable high- and low-pass (50-250 Hz) filters
Class AB design
CEA-2006 compliant
preamp inputs
fuse rating: 25A x 3
requires 8-gauge power and ground leads — wiring and hardware not included with amplifier
19"W x 1-11/16"H x 9-7/8"D

I was wondering if I could purchase components for the rear that had a 4ohm impedance but wire them in parallel so that they could be properly powered. I was considering Alpine SPS-600C or INFINITY 65.7CS 6.5" Kappa Component or INFINITY Kappa 60.9CS

 

Not a good idea, you would loose any ability the "stage" the system.

You also should not be putting tweeter behind you, they will interfere with staging and imaging, better to just get a set of mid-range/mid-bass drivers or just use the mids from a component set, wire them in series and connect them to the bridged rear channels of the amp for mono rear fill.

What is the make and model of your front speakers? 94

 

I have eclipse sp6510 components up front. But if I wire the rears in series and connect them in bridge wont that be 8ohms of impedance or is that okay since its bridged?

And yeah I was trying to avoid using the tweeters in the rear. Read up on how it causes imaging probs.

 

Well I did some reading and found out why to wire speakers in series. Essentially it increases the impedance which in turn lowers acoustical output, as in the case of rear-fill. Speaker output declines because the amplifier's power output decreases as the load impedance increases. and since its in bridged mode the 200rms will be lowered to closer to the speakers rated power... right?

If I wire the speakers in series am I still looking for speakers with a rated power around 65-75rms which is the power capability of my amp at 4ohms by 4 channels, I did some calculations and I would be making 50watts rms to each speaker if I wired them in sereis to the blaupunkt amp. I think thats right?

 

Yes, an 8 ohm load is OK for the amp.

Yes, the amps output will double when impedance is halved and conversely the amps output will be halved when impedance is doubled.

Yes the rear speakers would receive 1x100W RMS into an 8 ohm load, [or 50W each] with your amp.94