This has been my experience with using my stereo systems to amplify my digital keyboards. I actually liked the high fidelity sound that I got from my stereo speakers when running my keyboards through them. The sound was warm and smooth, and well . . . high fidelity. The main problem is matching the output signal (impedance I think) from your keyboard to the input requirements of your stereo receiver or power amp. As long as the impedance or levels are matched correctly, you should be able to get a good sound at a good volume from your home stereo system. I did this often when I lived in apartments or when I did not have keyboard amplifiers. Melodica-Me is right when he says you can get distortion from your stereo system if you are over driving the input.
I find that many (not all) combo amplifiers and powered monitors designed for high volume stage performance to be a bit rough with a slightly uneven or narrower frequency response when drive at high levels. Usually the cheaper equipment is worse, and even mid-level equipment can sound bad if over driven. Keyboard amps are supposed to be high fidelity, but the cheaper ones do not sound too good to me at high volume. As one blogger stated somewhere, “The only thing I would run through a Roland Keyboard is a chainsaw.” I get a chuckle out of that, but don’t take it too seriously if anyone owns a Roland amp.
At the same time, running a Fender electric piano (or digital electric piano) and some organs through a nice tube amp with some preamp, power amp, or speaker distortion is like heaven. I still have not have warmed up to the sound of my melodicas through a tube amp, even though I searched for that sweet spot for a long time.
To me, for a clean sound from a digital keyboard, one solution (beyond the home stereo) is to buy a powerful, high quality combo keyboard amp (like Melodica-Me’s Traynor) and run it on 2. But then you have to carry around 65 pounds of amplifier everywhere. Most keyboardist go through the house PA and hope the soundman and sound system are great.
Here is what I do for monitoring my Hammond organ at home or in a live setting when I don’t bring my Leslie out: I purchased a pair of JBL Eon, 12-inch, 2-way, bi-amped, solid state monitors/PA speakers about 8 years ago after demoing them. They sound as smooth as home stereo speakers unless cranked out on 10. I run my Hammond through both of them in stereo with the speakers pointed at my head. I can hear myself well, and I get a nice smooth sound that inspires me to play well. I try not to turn them up to the point where they sound rough.
Hey, didn’t we have a discussion like this like nine months ago or is my age or imagination at work? 🙂