There’s a long discussion in there I’ve begun reading. Not sure who/what is to blame, but the Windy website states:
WARNING: This item is not compatible with the GSCART switch as it cannot handle JAMMA audio and using these two items together could result in failure of the switch itself.
I’m not ruling this out if it otherwise works well (don’t own/plan to own a gscart). The disclaimer on the shmups thread may have been updated more recently than the site, appears to be worded differently and implying that all superguns may be a problem.
SUPERGUN WARNING: I had multiple units for the repair because of supergun damage. Whatever they do with supergun video/audio output – it’s wrong. I don’t own that thing and I don’t plan to look into it. I always stress that modded consoles are unsupported. In this particular case I won’t provide any support regarding supergun damage. You’ve been warned.
Did some searching and found this as I was typing:
The HAS is compatible with gscartsw. The issue discussed over at the shmupsforum was caused by improper setting of the audio, basically the JAMMA amplified audio was output directly to gscartsw.
The HAS attenuates the audio. However, just like the Windy Gaming supergun, it also gives you possibility to use JAMMA amplified audio. The difference is that in practice it’s impossible to switch to amplified audio by mistake, you’d really need to try hard, because the HAS uses two jumpers to set the audio level, instead of a simple switch.