Ok - for what it's worth...here's my 2 cents:
- the 5.1, 6.1 and 7.1 designations are only for home theatre set up. (The ".1 refers to the subwoofer and the number before that refers to the number of discrete speakers in addition to the sub)
- You DO NOT need anything like this in the garage - for hundreds of reasons.
- The ONLY thing you need/want for a garage is "stereo". (This is 2 discreet speakers and signals...same thing you get in a car - works with the "balance" functionality - move to the right the sound only comes from the right channel...back to the left, only from the left channel".
For a Garage, you aren't going to put your speakers in the acoustically correct location - instead, you will place them where they fit nicely. All of the home theatre specs above have VERY specific placement locations.
A Receiver is a unit that brings in signals and (usually) amplifies them so that they can be played over the speakers. High end systems will have seperate receivers and amplifiers...again, not important here.
Most receivers accept signals from multiple sources: Tape, CD, Record Player, iPod etc. The choices you have really depend on the age of the receiver and what was common today. If you're shopping new, CD and iPod will most certainly be included.
If you're looking for something more vintage - you can run a CD player into the older receiver (ditto with the iPod)...you'll just have to use the ports that were originally designed for something else (like a record player)
You didn't mention budget...speaker tech has come a long, long way. You can get monster sound out of small speakers today....whereas 25 years ago, the speaker cabinet also had to be big.
To be perfectly honest, you'd probably get plenty of sound out of this:
http://www.walmart.com/ip/iLive-Portable-Stereo-System-With-CD-Player-AM-FM-Radio-And-iPod-Dock/11008050
If you want something older for looks, nostalgia whatever, give us some more context and background - happy to help.