Forget the microfocuser, get a crayford, theres lots available from different manufacturers and I use a JMI EV1c on a fork mount. I can still swing the tube up to zenith with my 400D attached in alt/az mode as long as I do not attach a focal reducer. As you are using a GEM, clearence will not be an issue... (I generally use a wedge so clearence is also not an issue).
As I have said on another thread you can remove a heap of mirror flop by simply undoing the grub screws on the main focus knob and turning it clockwise until it bottoms out. Back it out a touch (1/8 turn), lock the screws and test for smoothness. If its ok leave it, if its a touch tight, back it off a little more. This has worked a treat for me and I only use the mirror lock if I plan to do long exposures. The R/ACF optics provide a nice flat field with good contrast. I have only noticed a slight tendency for bloating through the red filter but that may be caused by my dodgey focussing skills
. Blue/green/ha,0III and SII are all good as are single colour shots through the canon.