CVR12's

A mono amp is never useless for subs.  You would load the amp at 4 ohms (see woofer wiring diagrams at left).  The guys at work are telling you that you should load an amp at its limits of ability to get the most bang for the buck.  It is true that for 800 watts of power a 2 channel amp will cost you less.  That's because bridging a 4 ohm load across two channels is equivalent to a load of 2 ohms per channel...the amp's limit of ability.  The limit of most mono amps, being 1 channel, is also 2 ohms.

Some amps have more capability when it comes to handling large amounts of current flow.  Those that are 1 ohm stable are such amps.  Your subs can be wired down to a total 1 ohm load for use with these mono amps.  Keep in mind that you are still on the train of thought that loading an amplifier to its maximum ability is the way to go.  The performance for any of these amps is dirtiest that way but you get most watts for the money.  It all depends on your system goals.  You could easily just provide 500 watts to this pair of subs with clean power from a good mono amp at a load of 4 ohms and you'd benefit from the superior sound and cool-running amplifier, and did I mention very little draw on your car's electrical system.  You don't particularly NEED to provide 800 watts.

http://www.crutchfield.com/S-xCni61nXH50/cgi-bin/ProdView.asp?g=120&I=500MRDM105 is a nice amp for your subs.  And there are plenty of others from plenty of sellers.