The ASPI layer actually consists of 4 files
Apix.vxd
Aspienum.vxd
Wnaspi32.dll
Winaspi.dll
The full set 4.70 set is hard to track down and I can no longer find it on the web - if anyone wants it email me and I'll send it (40KB).
http://www.audioconverter.info/Q1002.php has a pointer to the Adaptec ASPI layer installer, but I'm not sure if it includes ALL the files.