Full description from the wikipedia:

"In 1998, Creative acquired Ensoniq Corporation, manufacturer of the AudioPCI, a card popular with OEMs at the time. It was a full-featured solution with wavetable MIDI (sample-based synthesizer), 4-speaker DirectSound3D surround sound, A3D emulation and full DOS legacy support. It was cheap due to lack of hardware acceleration. It is full-duplex but at least in MS Windows cannot play back several sources at once.

Creative released many cards using the original AudioPCI chip, Ensoniq ES1370, and several boards using revised versions of this chip (ES1371 and ES1373), and some with relabeled AudioPCI chips (they say Creative on them.) Boards using AudioPCI tech are usually easily identifiable by the board design and the chip size because they all look quite similar. Such boards include Sound Blaster PCI64 (April 1998), PCI128 (July 1998), Creative Ensoniq AudioPCI, Vibra PCI and Sound Blaster 16 PCI.

An ES137x chip contains 3 stereo sample rate converters, some buffers and a PCI busmaster interface. Analogue interfacing is done by a codec chip, which runs at a fixed sampling frequency of 44 (Ensoniq Audio PCI) or 48 kHz (Creative's versions). (ISA soundcards had not resampled but switched between different time bases.) ES137x do not support SoundFonts but a filter-less MIDI engine with wavetable (sample table) sets of 2, 4, and 8MB size."

Does anyone know the file format for the MIDI sound banks on these cards?