(edited my post, sorry for the wall of text everyone)
I wouldn't say ASIO doesn't work in OBS-MP. OBS may not have native support for ASIO, but I'm not sure I really needs to, as long as you can get the audio IN/OUT of OBS with Virtual Audio Cable, VB Cable, etc.
I got VSTHost with some Reaper plugins working initially using MME-type Wave device inputs and outputs - almost perfectly - in a relatively short amount of time. I also found ReaFir to be pretty good for noise reduction/removal, and with the amount of fan noise I have in my computer room, I needed more than EQ, Noise Gate and Compressor.
Overall I was quite impressed with the results of my AT2020USB+ mic input after running it through the collection of Reaper plugins I had put together based on this tutorial youtube video I found:
https://www.youtube.com/watch?v=gIv3gdF9l5M
I DID have a pretty big problem with "lip sync" between the between mic input and webcam when I first got VSTHost and the plugins I used working, and the amount of audio +/- delay needed to get them back in sync was not the same with each recording.
Switching from MME Wave devices for input and output to ASIO4ALL took care of that and the stream mic is perfectly in sync with the webcam now without having to adjust +/- delay at all.
I do have one problem left to figure out, brief drop-outs of game sound from the sound card in OBS recordings that I am pretty sure don't actually happen in-game. This is a little odd since I am only using ASIO and VAC for the mics, not audio output from my onboard sound, but if it's not some weird problem with OBS then it might have to do with needing to adjust ASIO and device buffers.
But other than that, using ASIO4ALL2 and VAC with VSTHost and the plugins mentioned in that dude's youtube video seems to be a LOT better on latency for cleaning up the mic input.
Cheers