Is there anything not right about using a stereo system to amplify a keyboard? When I was young I plugged all manner of things into my dad's Dynaco pre-amp and my Harmon-Kardon 430 receiver, guitars, mics, tape recorders, etc. Nothing blew out.
Now, an electronic keyboard (kids') needs amplification and I'm tempted to use a Creek 4140 integrated through one of it's inputs other than the phono. Alternatively the BH Quickie that needs building feeding a stock Dynaco ST-70 is an option (or just the ST-70 with a volume pot installed.)
Then, the other advice I'd appreciate would be recommendations for an inexpensive kit or DIY approach to stereo keyboard amplification for practice/small space/near-field setup. The music stores have manufactured small monitor speakers in use for demoing gear that could be part of the solution.