Modern MSX-Audio cartridges

https://www.msx.org/wiki/Category:OPL4

Original Moonsound is EOL because Sunrise's halted activities, several years ago.

Tecnobytes is gathering a list of people interested in a new batch of their MSX Audio product:

http://www.tecnobytes.com.br/2021/03/audiowave-msx-audio-pre...

Now, about OPL4, seems like the only option is to buy a a GR8NET and use it in OPL4 mode, can't see anyone having it on stock. GR8NET emulates it over FPGA, but Eugeny is quite a hard worker on getting things working properly, so even though not a real OPL4, I would think it should already be working quite close to the real thing and if not, it will in the near future.

GR8NET is proprietary

Well, it won't hurt sending them an e-mail, you never know when someone change their mind and decide to no longer buy and ask them if they can look for someone else to fill in or if they end-up being able to produce some spare devices... Anyway, yeah, ultimately it is quite difficult, even though I rarely use it, I keep my OPL4 Shock Wave with me just because it is really difficult to find those being sold, be it new or used. Good luck, hope you find what you are looking for.

Ebsoft.fr had a wozblaster kit for sale last year but i missed it... In terms of software support, which standard would you say is more popular - msx-audio or moonsound? The latter is obviously higher quality, but i suppose a lot more titles have options for msx-music FM synthesis at least.

I think that first you should tell us what you expect to achieve with those expansions...

If for gaming, a few have MSX Audio, a few homebrews have OPL4 support (and most of them support MSX Audio as well), but I don't think it is worth the trouble just for that, OpenMSX can serve you well if you are just curious about those few games sound tracks

If for using it to make tracks, or playing back sound tracks, etc... MSX Audio has more support, but like Parn said, OPL4 has been gaining traction... If your intention is to have fun for yourself, then I would go through OPL4 route... If you plan to share and want to have some audience, MSX Audio...

I don't think that there is an universal response, you have to think about it and make a choice that is best for you.