You're referring to the MB Quart SBR 250.92? I think that one's strictly a 6 ohm single voice coil sub, I could be wrong though. On a single channel, whatever your amp is rated at 4 ohms, knock that rating down to 75% and that's about what you're going to get (if it's a single voice coil). Your amp is going to run a bit cooler.
If you're going to power the sub by bridging your amp, (if it is only a single voice coil 6 ohm sub) then each channel will see a 3 ohm load, so as long as each channel can handle at least a two ohm load, you should be fine. Again, take the bridged wattage, of 4 ohms normally, and knock it down to 75%. Really, however, that sub only takes about 175 watts maximum, so don't overpower it. The RMS is what you should be trying to match on both, not the peak power.