An 040 can probably handle MPEG decoding at full quality... if you don't do anything else at the same time. But remember melodympeg.device? In AMPlifier's MPEG player prefs, on the decoder tab, set playback to Hardware and type in melodympeg.device. That'll offload decoding to the Melody board, freeing your CPU and allowing you to multitask.
If you're working on a machine without an MPEG decoder, also play with the Samplerate and Quality cycle gadgets in AMPlifier, and the output rate in AHI prefs.
AHI 6 requires an 020, while AHI 4 could use a plain 000. Not sure if that translates directly into more CPU usage on better processors, but it's a possibility.
EDIT: Whoops, just saw you're using a Toccata and not the Melody. Still, the Samplerate, Quality, and output rate settings should suffice to get you balanced between quality and speed.
