There have been a number of post in the past re HoonTech AudioDSP24. I even bought one of them 6 months ago by could never make it to output AC3 or DTS via S/P-DIF (using PowerDVD 2.55, not yet tried with v3)
There are also very slow in coming with Win2000 drivers but there are not unique in that respect.
I was told by the distributor in Europe that this cards are now bundled with PowerDVD (don't know which version). So maybe the AC3 output is now sorted out.