I have 3.1 speaker system that is 6 ohms. SS-MSP66SL, SS-MSP66SR, SS-CNP66, and Sub SS-WMSP66. I was thinking of getting these Sony SSF-5000. I was going to use the floor standing ones as the front and the other two as the rear. I know that I would have to use a different center (8 ohms). But will this work overall and could I use the subwoofer.
The amplifiers/receivers mentioned above are good ones, if you want to go with higher model then its better. But if you are looking for a sub-amp then I would suggest getting a powered/amplified sub-woofer but what is your budget and listening preference? Hip hop, classical etc.?
... The amps that I have seen are like the ones I see in cars. Are those the right ones?
It's all depends... Are you talking about car amplifiers? If you have something to power them with, then sure! But those are difficult to manage; better stick with home appliances, especially if you are thinking about 5.1 surround sound. So then you need to budget a receiver for your existing speakers plus an amplified sub-woofer. So depending on where you're located. Some equipment may be too expensive to acquire.
Denon AVR1610 is the old model and new one is Denon AVR1611 are good recievers. Link below is for amplified subwoofers but the Velodyne sub is my first pick.