I have an ONKYO TX-DS575X receiver and this 8" passive sub from a car, shown here http://goo.gl/8xbCt . The sub has a 4 ohm impedence, and the mininum (recommended) for my receiver is 6, or I'd just plug it into a front channel. The receiver has a subwoofer pre-out, so I guess my question is what would be the cheapest amplifier (plate amp? idk) that would be compatible with my sub, and specifically how it would be wired.
Would I need to bridge left and right to both go to sub or just go from one?
Yes, you could use that amp. Connect the Onkyo's 'Sub Pre Out' to one, (just one: Left or Right), input connector on the amp and hook up your sub to the corresponding speaker output. There is no indication that that Pyle amp is bridgeable; one channel would be unused but that shouldn't be no problem.
There are, of course, various 1-channel, (i.e. mono or monoblock), amps available for home use. But frankly I wouldn't throw to much money at a amp to drive that particular speaker; instead I'd look for a low-cost self-power home-type subwoofer. Even something as low cost as this Polk PSW10, (see HERE), would be an improvement.
I agree with Bill. Don't throw good money after bad.
For starters, that sub enclosure was designed to work in the small environment of a car interior. IT won't be anywhere near as efficient when you move it ito a room where a lot of ai lot moore air needs to be moved.
ikewise, those pile ....err, Pyle amps are rated in a totally unethical manner. Any power rating that doesn't specify a frequency range or distortion level is hiding something. My $$ is that it's rated at 10% but without a model number to reference it's difficult to find any meaningful information.
I honestly think that, for the money, you would be far better off saving up and getting that Polk sub he suggested. I got one for a friend and, for the $$, it ain't bad at all. Guarantee it'll be light years ahead of where you're heading now.
I can't find your amp listed at pile's site, but I did stumble across this "150 watt amplifier". Take a close look at it's power spec. Any reputable company might rate this at 15 watts but, then again, without seeing a distortion/frequency range, I wouldn't even count on that 15 watts being clean.
Oh, and for future reference, you can't assume that just any stereo amp can be bridged. Well, maybe you can, but many will release their magic smoke and die.