I too am very interested in an emulator for the Mitsumi 2.8" drive.
I am an existing customer with an HxC for an Emax, and would like a solution to replace the Mitsumi 2.8" drive in my Akai S700 sampler.
These drives are also found in the Roland S-10, MKS100 and S-220, Korg SQ1-D and SQD-8, Akai S700 and X7000, and the Yamaha MDF1.
Most notably, they are used in the Nintendo Famicon gaming system, which has a large and loyal community of supporters.
The original drive from Mitsumi has a rubber drive belt that fails over time, rendering the device inoperable. Replacing the belt requires disassembly of much of the drive mechanism, and it is often necessary to re-align the head after replacement.
I would be willing to assist in design, development, or troubleshooting of such a project.
There is a great deal of technical information on the Mistumi QD drive included in documents on the Nintendo Famicon System - some of the information explains the interface between the game system and the disk controller, yet some of the information focuses on the disk and data structure.
Please contact me if you would like to explore this further.
Here are a few links:
http://nesdev.com/FDS%20technical%20reference.txt - Technical Reference
http://nesdev.com/fdsloadr.zip - This zip file contains the source code for a PC-based disk emulator for the Mitsumi drive, as well as a text description of its operation and electrical connection to the parallel port
-Randel