I'm not familiar with the Microplex CD2408(or anything from Microplex).
Now, assuming that the Microplex is using it's own proprietary language and/or protocol AND that it will translate incoming DMX-512 signalling to it's own scheme, then there's no valid reason why MyDMX or any other software or DMX controller shouldn't work.
So, assuming what I am assuming is correct, then it may be safe to assume that what you're assuming would also be correct. Or so I would assume. Assuming we're all correct. That's a lot of assumption.
Honestly, you might be better off migrating off the Microplex stuff and move to ADJ or Elation dimmer packs, or maybe even move to LED fixtures. I think going forward, it would be in the best interest to at least go with DMX-512 gear. I don't mean exclusively, if you find a high-tech effect, you can power it on/off with a switching pack, or setting a DP-DMX20L channel into switching mode.
Not to sort of throw numbers out, but you could get two DP-DMX20L's to get your 8 channels(which could support up to 16 fixtures), and then make a choice of a basic DMX controller or MyDMX software. For a "Fixed/in-place system", I personally recommend a controller. You can bolt it in place, and including a "Cheat sheet" that contains usage operations and what is programmed where. If you leave the DMX connection accessible, you can always patch in something like MyDMX should you need to.