I was surprised to see that it wasn't listed in the Logitech database. Are you sure that your remote is defective and that the problem is not in the preamp's IR receiver? One way to check might be if you can find a Threshold dealer with a functioning remote, or a preamp on which you could test your remote.
Threshold Stasis 5.0 preamp
I bought this second hand, but the supplied remote does not work
I have emailed Threshold for a remote or the hex codes, but they refused to help
Can anyone assist as it is not on Logitech data base (for example)?
If I knew the hex codes I can get a remote purpose built, but fat chance if Threshold are being pillocks