I just got the same soundcard, so glad I came across the post! Did you the wavetable header working perchance? I've not tried yet, but saw in those jumper settings that none of them seem to mention separate wavetable IRQs or addresses...

Just got myself an Amstrad PC5286HD Although I had one as a kid. Basic cleaning, repairing and making-useful type of job to amuse me during these coronatimes. Thought I'd post a link to my log here, as there is very little content for this machine out there. Plus I'm quite sure I'll be hitting you …