Quick Amp question - Soundstream VGA320.4

[Mike in Boston]

This amp looks like it'll fit my needs and price for powering a set of 6 1/2" components and a set of 8" subs. My question is (since my amp experience is low) do I need a head unit with 3 RCA outs for the subs or can I set away with 2 RCA outs? Do amp crossovers usually work for all channels or just in channel pairs? Could I get away with a single pair of RCA outs and use the pre-amp out on the amp itself to feed the other 2 channels? Do most amps no-a-days have pre-amp RCA outs like this one? I'm a little lost Any advice would be great! Thanks, Mike