Phew-- I been looking at the interent for a couple hours now trying to figure out the answer to this question, and I've learned a lot from this site... but I don't think I've quite learned exactly what I want to know. So I'ma ask you all point-blank: I have a 4-ohm Ampeg 4x10 cab and an 8-ohm custom cab with a 18" Eminence speaker in it. I also have an Tech 21 RBI pre-amp. I want to buy a power amp and a crossover so I can run these two cabinets together using the 18 for the lows and the 4x10 for the highs. I'm looking at Crest and Crown power amps, but how do I figure out what amp will supply each cab with enough power? The 4x10 runs at 600 watts RMS and the 18 runs 800 watts RMS-- so, do I want a power amp that will give me at least 800 watts to 8 ohms in stereo? I used to run just the 4x10 off a 350-watt Ampeg SVT head but I felt like it just wasn't loud enough to fill up the big barn I practice in, so I'm trying to get into a situation where I've got more than enough volume for each of these speakers... does that make sense? Reading about ohms and stereo and parallel and etc all day has made my brain a little mushy.