I wanted to provide a little update... I've had my Casio PX 150 for about a week and a half now. Initially I was quite disappointed with the onboard speakers. Thanks to a helpful suggestion from the forum, the sound improved quite a bit after reducing the `Brightness` setting. But it was still lackluster compared to any kind of headphones.
Then I thought well what the heck, let me try my PC speaker setup; a Logitech X530 5.1 combo I bought years ago for under 50 bucks. I just took the front two speakers and the sub, basically making this the Logitech X230 setup. And wow... the sound is SO much better, even with these budget speakers. More mellow, and with actual oomph for the bass strings! The `subwoofer` is only a 5.5" but it actually manages very well. Sounds more like a real piano now
Searching the web, it sounds like the Logitech models from a couple years ago were a VERY good buy. Then Logitech realized what they had on their hands, and comparable models are now much more expensive.
So now I'm thinking I might look on eBay for a used Z2300 set. It received really good reviews on this forum, and comes with a serious sub. I wonder how that would compare to a $200 set of monitors.
Overall I'm real happy with the PX150 now, especially with the better speaker setup. The action is really good, I like the simulated ivory & ebony, and construction is very solid (especially with the CS67 stand). There seems to be just the slightest of cabinet vibration on two of the keys, but it's not noticeable 90% of the time. All in all, love this setup