I don't think you'll have much luck in getting the source code, seeing how the developers are nowhere to be found, and the homepage has long since died.
Then again, this is just my opinion. I'm more interested in asking why would anyone do anything with a variant of UltraHLE that nearly everybody stopped using 6 years ago.
You'll be better off getting a new PC, any current cheap computer will do better than such an old PC.Because I want to play Goldeneye full speed on 13 year old hardware. Using a separate audio plugin from what is included with UHLE is necessary to prevent an audio related crash in Goldeneye. UHLE 2064 has the plugin spec and some other optimizations.
Please let someone who can vouch for the source code's whereabouts tell me if it's been found or not.
Advice on splitting the sound code off into a plugin would be great help if source code can't be found.
And literally it's just for Goldeneye.