As for the double pal/productivity mode hack for the 32khz screen modes...well few people could use those modes on their Amiga and games or demos would run slower if used as it massively saps CPU time doesn't it? So dead end really in reality unless you want a blank screen when playing mods..
I thought we were talking about sound samples, not demo productions/mods.
A standard 68000 ECS Amiga such as the A500+ can play samples at 56KHz, if in a double line mode. And the Workbench screen wouldn't disappear either.
@BOOtDisk
Yes, with the CyberSound driver you can get 14bit stereo audio from Paula, and at 56KHz if in a double line mode. So playing cd's/16bit audio sounds really good, as the samples don't have to be downsampled at all (Paula will play them at 44.1KHz), scaled down to 14bits (68020 required for CyberSound).
You can try this out yourself if you like as it's included in the Play16 package:
http://aminet.net/package/mus/play/Play16