Make sure your MIDI setup is as follows:

In the "IN 'ALL MIDI INPUTS'" column - the "Yamaha MOXF6/MOXF8-1" (port 1) is marked. This is the PORT on which the MOXF will communicate musical MIDI data to and receive data from the computer. Only PORTS that are legitimate MIDI INPUT devices should be marked here. Of the Ports appearing for the MOXF6/MOXF8 only Port 1 concerns the MOXF as a Input device. If you connect an external controller device to the MOXF's 5-pin MIDI IN jack, you would mark "Yamaha MOXF6/MOXF8-3" (port 3). But nothing but the specific MIDI ports that send Note-on, data should be marked!

When you say you set the sample rate, we’re sure you mean Buffer Size... in general, set this whatever your computer needs to deliver click and pop free audio. You are working with hardware, you will be monitoring yourself direct so the latency will not be an issue.

Increase the Buffer Size, as necessary, to get rid of the clicks and pops.

for some reason, the driver keeps malfunctioning/ disappearing from my system/sounds (doesn't always show in my Device Manager). This is relatively new but of course I have NO USB-sourced sound from the MoXF. I've Uninstalled / Reinstalled the driver to no avail. I did have it working for a few moments and increased the Buffer size up to 1024, but still got the pops. Now I have nothing. I even tried the 1.10.3 version with similar results. Maybe something I should totally CLEAN from my PC to allow the driver to stabilize??

The driver is steady and has 6 years running the MOXF. And literally thousands of folks using it. You have something that is causing a conflict... we would have no way of knowing what in your computer setup (unless you tell us). If you set the Buffer Size to 1024 and are still getting clicks and pops you can be happy that it is not issue with processing speed of your computer. Those clicks and pops are being caused elsewhere (stop installing the driver over and over...)

Can you describe your system. What’s configured? What’s acting as your audio interface? Where are your studio monitors connected - to what device? What other gear is connected and how? Let us know.

I must have held my mouth properly today as the driver is working with my moxF again. I think Windows leaves "remnants" of past installations. and that could have well been my issue that microsoft resolved "on its own" (?) Buffer is 512 w ~40 msec Total latency, (which I hope doesn't hinder my recording).

My configuration is shown in these two attachments.

One more question if I may: I assume the Yamaha-Steinberg driver is an ASIO driver? Esp. since both were developed by Steinberg.

Yes, the Yamaha Steinberg Driver is an ASIO driver. The other thing you might want to consider is trying just the MOXF connected without the Keystep connected just to see if there might be a conflict. Just a thought.