Help: MediaMonkey to JRiver?

Yup, just let jriver build it's own db by pointing it at your files. You can give it a try for free and run it without bailing on MM until you are sure you like it.
As an aside, have you tried deleting your old MM db and rebuilding it? There might be some corruption in the db causing your buggy-ness.

One of the things JRiver excels at is file management and customizations for music library management. But, it does take a while to figure out what it is capable of. To get started, I'd recommend copying 50 albums or so to a separate folder and pointing JRiver only at that folder. Learn how things work with JRiver before using it with your whole media library. I've found it to be very stable, but it does take a while to learn.

I switched from Media Monkey and iTunes several years ago. The transition was without major problems, but it did take a while to figure out what JRiver is capable of. It is not short of options! I have a sense I'm only using half of what it can do.

I'm not sure how it handles ratings that are placed by another program as I've never paid attention to that feature. One problem I did have was tagging artwork when a track has a long file name ending with a punctuation mark of some sort. That was a head scratcher, but I finally figured out that the file name was the problem on a handful of tracks. JRiver allows a user to set up any file naming convention. I use the music folder name/artist name/album name/track # plus track name. As long as the tagging is done consistently, file management is a breeze this way.

If you find you like how JRiver works after playing with it for a while, I'd recommend setting it up to import all of the files in your music folder to its library structure, then manage the files after that. I'm at around 30K tracks in mine. It won't move tracks around into different folder structures unless you tell the program to do that. I would recommend using one program exclusively though once you settle on what works best for you. Easier to manage things that way.

Since Emlyn mentioned how you might run into an issue with ratings i'll add my 2 cents: transferring ratings rarely happens smoothly with any software out there.

Easy fix: create m3u playlists in MM for each rating (5 stars, 4 stars...) and then import those into JR. Then you can just select all tracks within that Playlist and rate them accordingly. Quick, painless process.

JR is indeed extremely powerful. You can create your own tags (i.e. sub-genres), use regular expressions inside tags, import all sort of track info from allmusic.Com through a plugin, etc...

Best of all, any tagging is properly saved inside the music file.

I used to spend a lot of time in JR and loved it. I had made a few themes for it back in the day. It was fun

I started using Jriver earlier this year after using MM for years and haven't had many problems. I think it sounds better than MM. I don't use ratings so can't help you there. You don't need to wipe anything. Let Jriver find your music and create the dll files like MM to use the music on your hard drive. The only thing I haven't figured out is how to remove the "The" in "The Rolling Stones" ect so it will be in the R list, not in the T list. I also want to figure out how to get Jriver to send DSD to my dac and hear if that sounds better.

jremote works great. Superior to the Logitech software I use in every way.