2 ohms is the minimum load for a coliseum. Minimum doesn't imply correct. It will work fine with a 4 ohm cabinet. Yes, the output power will be reduced by about 65% of whatever the 2 ohm rating is, but that would be less than 3 db and most people won't hear the difference. If you want volume, forget power and ohmage and go for more efficiency in your speakers - way more bang for the buck.
The 880 is the 880 because that is the rating of the coliseum in "peak watts". Peak watts can be determined by whatever means the manufacturer wants to use. I've seen several 25 watts (RMS) being advertised as 4-500 watt amps.
Even RMS is not standardized, but it is the closest we have between manufacturers. The primary difference between manufacturers is the distortion level at which they use to measure the RMS output.
The test is easy... it is either loud enough or it ain't. If it ain't, go for more effecient speakers... or look for a 10X more powerful amp and hope you don't blow out your existing speakers using it.