Yes, the Roland RD170 is a better bet for you if spending just a little more money won't hurt. Also, you shouldn't use your guitar amp if you want accurate reproduction of keyboard sounds.
Behringer has come out with a powered speaker stereo system which has 15 watts per side and sells for around $60.00 for the whole system. It takes two stereo sources plus a mic input with it's own volume control.
If you want something better, Roland has the DM-20's which are a little more powerful, about the same size and sell for $199.00. I would also recommend the Behringer Truth B2030 powered stereo monitors. These have 110 watts per speaker and sell for $279.00 per pair. All these would work fine for home. There are other options for performing such as keybaord amps from Roland starting at about $229.00 and up.
George Kaye
Kaye's Music Scene
Reseda, California
818-881-5566