Yea, skip the mx4sio and switch if you plan on using MMCE via MemCardPro 2, SD2PSX, or PSXMemCard Gen2.
If you use a FMCB card you have USB or SMB to load backups. MMCE is even better than MX4SIO anyways.
These are a lot of fun! Share pics, I'd like to see your build when you're done!!