Well, here's the Windows 7 Ultimate 64-bit, with my test run of Dosbox - D-Fend Reloaded 0.82 package, passing the midi to the MT-32 module via X-Fi's I/O drive.

Everything works just like it did with my Vista Ultimate 64-bit, which I'm still having on another 500GB HDD.

My Vista Ultimate 64-bit - Dosbox - MT-32 combo setup can be found here.

The white cable with green connector cover is the line which recieves the midi output from the MT-32 and back to the Line IN/2 of the X-Fi.
By this method, you don't need to keep 2 separate speaker sets for sound effects and midi. You can hear both the sfx and midi music via the same x-fi's playback. The mic gain knob next to the line2 input jack can get the boost required from the mt-32.

The left wire which has a meshwork of red and black and green is the co-axial line for listening to digital sounds- like Dolby DTS/Digital/ ProLogicII, etc., which is connected to the SR5200 receiver at the far left below.

The right cable (black) is the midi OUT to the MT-32. The midi message from the game, like the Sierra's Conquests of the Longbow shown above, goes via the dosbox ( route the message after finding out the channel number by using the dosbox command "mixer /listmidi".), through the X-Fi's MIDI port, through this midi cable, to the MT-32, and from MT-32b back to the X-Fi's line in port.

My system setup :

ASUS Striker II Formula
intel Quad-core Q9300
4GB DDR2 @ 1066MHz
2.32TB SATA II HDD (500GB WinXP Pro, 500GB Vista Ultimate x64, 1TB RAID for Windows 7 Ultimate 64-bit, plus 1 320GB IDE with some downloaded and misc. files.)
Geforce 9800GTX x2 SLI
X-Fi Platinum configured to output at 7.1 channels
2 DVD-RAM Drives
1 3.5" FDD
Marantz SR5200 Surround Reciever with 7.1ch support
BenQ DV3750 37" LCD Full HD.
CoolerMaster Gemini II Heatsink with 2 CPU 120mm fans
7 other internal casing fans - all silent
Plus 1 CoolerMaster Cross-Flow fan - fits into the full tower CM Stacker chassis. The cross flow fan blows beneath the motherboard, in between the casing and the mobo.

It's not the latest system, but able to use the 64-bit OSs smoothly and without hiccups.

My Opinion of the Windows 7 Ultimate x64?

1. Faster. Much Faster in Operation, Loading Time, program executions, when compared to the Vista Ultimate x64.

2. The Dosbox passes the midi message from the game to the MT-32 via the X-Fi's I/O Drive just like it did with Vista x64.

3.Many subtle and substantial improvements over Vista.

My only gripe with Windows 7 is , it's so similar to Vista, cosmetically. If you've seen or have Vista, there's nothing much here to differentiate, except for those subtle changes and improvements. Like the AeroShake, for instance.

On the other hand, would I continue using Vista? - Maybe.

Windows 7? - Definitely! (It's quite nice! 😁)

XP? Oh yes, I can't let it go! It's my favourite of the MS's OSs. 😀

Things to check out for me : Haven't tested the native 3D support. (Vista required Creative's Alchemy software to enable the 3D sounds.)
Have to try and install Diablo2 and see without Alchemy.