It is a shame that instead of solving your problem (which has nothing to do with an electronic focuser), you are instead told to buy more ZWO devices, specifically the ZWO electronic focuser, which will not solve your immediate problem anyway.
If I understand your original post correctly, you took your eyepiece out of the Meade microfocuser,and replaced the eyepiece with a ZWO camera, and all you get is a donut on the screen, correct?
If that is so, read on. If that was not your original problem, then please ignore.
By the way, I had bought one of the "limited edition" 8" LX-200 GPS back in about year 2000, and of course I bought a Meade zero image shift microfocuser, too. The optics was natively f/6.3 and with the reducer, became a whopping f/4.
That kind of f number was nothing short of a miracle in the days before Hyperstar, and it was virtually impossible to focus well with the main focus knob.
They stopped manufacturing it soon after because it was way too expensive to produce an f/6.3 SCT. I have stopped using it a long time ago because I no longer can handle heavy OTA even though it is on its wheeley in the family room (I am over 70 years old and short).
Anyhow back to your problem....
Your problem has nothing to do with your microfocuser; it is simply that your camera and your eyepiece are not parfocal (don't have the focus positions).
The fact that you can see a white donut with a hole in the middle is really promising. It says you are not too overexposed and you have an image to focus with.
The first thing is to ignore the microfocuser for the moment, it will not have the range to handle such a large out of focus image.
Chances are that you are far away from parfocus. The donut you see is basically a very out of focus image of the entrance pupil of your OTA and the dark hole is the shadow of the secondary.
So, what you need to do is use the main focuser knob (the one that moves the mirror) to bring the SCT to focus on to the camera sensor.
Turn the main focusing knob to reduce the size of the donut. Again, it is very good that you at least see a donut so you know which direction to turn the knob.
Keep turning to get the donut to be smaller. In the meantime you will also need to reduce exposure time so that the donut is not overexposed. When the donut is small enough, you should be able to see real images appearing and you can finish focus on a real image. If you are pointed to a star, you should start seeing Airy rings around the hole as you get close to focus, assuming the air is very steady.
This should get you going.
Once the main focus knob is mostly focused, you can now use your microfocuser to really focus well.
Now, if you want the eyepiece and the camera to be parfocal, so you can exchange them and just need to fine focus with the microfocuser and not touch the main focus knob, you will need to add spacers to your eyepiece holder or to the camera, depending on who needs to be further from the metal back of your OTA.
Remember to reduce exposure time as you get into focus. Modern cameras are very sensitive. Something like Sirius will overexpose the camera with just a 0.1 second exposure.
If all that works, we can then fine tune to get the flattest image possible for your telescope. Read up on "field curvature" if you need to know more.
If memory serves, the Meade 8" SCT requires a backfocus of 105mm to get a good flat field.
Basically this is the distance that the sensor needs to be placed behind the OTA. If you read the ASI178 documentation, the top of the "T2 ring" is 17.5mm away from the camera's sensor. This means that you want to add spacers so that the metal back of the OTA (the metal interface between the microfocuser and the OTA body) is exactly 105-17.5 = 87.5mm from the front of the T2 Ring of the camera. If you add a glass filter in between, you will need to add about an additional millimeter to the optical back focus.
If this proper backfocus is not used, you will find image distortions at the edges of the image when the center of the image is in focus (cause by field curvature).
Try to get the backfocus to within 1mm of what the manufacturer specifies, if you can. 10mm off is too much off. 2mm is acceptable if you don't care if the stars at the corners of the image is tack sharp.
In the future, if you want to go ahead an install an electronic focuser that you can control by ASIAIR, only then do you need to buy a ZWO EAF, together with a ZWO bracket to attach the EAF to the Meade. Most programs (except ASIAIR) knows how to talk to the Meade microfocuser, so you won't ever need the ZWO EAF unless you are hell bent on using the ASIAIR.
Get an RMA anyway, to keep your options open.