I want to know there is any add-on board for OPL4 cartridge to use MSX-AUDIO BIOS v1.3.
If exists, what purpose for? Any software for that?
Thank you for keeping an eye on this thread and making yourself available to discuss improvements to your project. My two cents: I personally like the idea of having ADPCM support on an OPL4 cartridge, especially because MSX-Audio cartridges aren't easy (or inexpensive) to come by in my country. But I also believe it isn't worth the extra cost, if it can't be done with a cheaper FPGA.
About a BIOS add-on board, it doesn't exist yet... For now. I'm trying to help in making one, but due to unforeseen circumstances the project is delayed. I'm not a hardware person, though, and so far I just simulated the hardware and some of the software in OpenMSX, and it works fine. Rune Master II and Firehawk HDD sound just awesome with it. The main difference is that the music sounds much less noisy (instruments are synthesized in a higher resolution), which is very noticeable in the bass instruments. But really, everything sounds just nice.
As far as I recall, those who tested the FireHawk HDD being played in stereo in the OPL3 cartridge were very impressed.
...but no footage of that on YouTube... sniff...
For the time being, I could demonstrate it with OpenMSX. If you want to see it in real hardware, I hope we can arrange it before the end of February. 
Thank you, all your advice is valuable to me.
As expected, there are various preferences and that's natural I think.
What I can tell you at this moment, is that I will make a DalSoRi v2 with following specifications:
OPL4 (YMF278B)
YRW801M sample ROM
4MB sample RAM (upgraded from v1)
128KB (or more) BIOS ROM (new from v1)
8KB (or more) BIOS RAM (new from v1)
Audio DAC, Headphone amplifier, 3.5" phone jack
Switch to disable BIOS ROM/RAM (new from v1)
Konami-size (fit into Overrich case)
This is good opportunity for people who doesn't have a DalSoRi v1 but has MSX-AUDIO.
Also for people who doesn't have a DalSoRi v1 and don't want any other functions.
You don't need to worry about the compatibility problem between v1 and v2.
I'll finish the development of DalSoRi v2 until the next month since it's not difficult.
Yeah, No ADPCM. Well, what for ones who want MSX-AUDIO functionality?
I think this needs more discussions. Exactly what parts of MSX-AUDIO functionalities are need, is not determined yet.
I also must determine the approach to implement the functions. So I need evaluation period more.
DalSoRi v2 will have following dedicated registers. That's based on the sd_snatcherer's suggestion but little bit different.
60xxH: flash memory banking register 0 (default: 0)
61xxH: flash memory banking register 1 (default: 1)
62xxH: flash memory banking register 2 (default: 2)
63xxH: flash memory banking register 3 (default: 3)
64xxH: SRAM memory banking register (default: 0)
[3:0] - SRAM segment
[7:4] - SRAM disable (1: disable)
67xxH: configuration register (default: 0)
[0] - enable FM I/O port map to C0H-C3H
[1] - disable FM I/O port map to C4H-C7H
[2] - reserved (must write 0)
[3] - reserved (must write 0)
[4] - enable flash memory write
[5] - enable 2MB sample RAM instead of YRW801M
[6] - reserved (must write 0)
[7] - reserved (must write 0)
If there is anything I missed, let me know.
Let's see what I can do with v2 in the next month. If I feel fun with it, I'll continue to develop v2.5 or v3.0
If almost all software use BIOS instead of I/O ports, can't the BIOS emulate ADPCM through OPL4 ?
Any question and suggestion is welcome always!
Jun
Ok for me for this DalSoRi v2 (missed the v1)
You can add me to your customers list 
