Here's another portable kb monitor system option worth looking into:

Cambridge Soundworks Model Twelve

Has anyone here heard these?
http://www.hifi.com/store/category.cgi?category=search&item=c1md12ee&type=store

I have a friend who had to fly across Country (before 9/11/2001) to perform for an exclusive small private party at a swanky home. He said the Model Twelve was the perfect solution as the entire portable speaker system (satelite speakers, control module, and subwoofer all fit in its built in small compact carrying case with handle: total 26 lbs) stores easily under the airline seat. He told me the sound quality and volume was more than suficient for this setting. I realize that this setup may not be as quick & convenient as having built in speakers in your kb, but, it might be the next best convenient thing because its sub Woofer doubles as a carry case for the entire system. This could work out as a nice personal monitoring solution for the speakerless Yamaha Tyros as both the Tyros & Model 12 system weigh about the same: making for a nice balancing act . . . one in each hand.

- Scott

PS: Flea, of the Red Hot Chilli Peppers, claims that the Model 12 is the best traveling sound system he's ever heard and that they take it everywhere they go. The Model 12 also received the 'editors choice' award by PC Magazine for whatever that's worth.