Since I went through a DP testing process for my recent purchase, I have a little something to share on the testing process. This applies pretty much only to those who are looking for an acoustic substitute - it's not about testing the techno features.

1. If you can play (no matter how good or how rusty), bring some score with you or use something at the store. Play passages of different nature - slow, fast, lively, grand, with and without pedal, etc. and try to select music that covers a good range of octaves. I find that playing the same several pieces (or same passages) on different pianos is much more "informative" to the fingers and the ears than just playing some single notes or chords or scales. This has helped me discern the differences a lot more easily.

2. If you have good headphones, bring them so you can really hear the sound over the noise in the store. Since the acoustics (or lack of!) from store to store is different, your same pair of headphones will let you compare apples to apples. Of course you still want to hear the sound straight from the speakers for speaker sound quality.

3. I find the demo songs minimally useful, except perhaps as a way to hear the speaker system.

These may be obvious points, but it didn't occur to me to do it this way at first. When I started testing this way, the models that appeal to me became clear pretty quickly.

Happy testing to y'all!