You current MSI Mobo looks plenty good to me. The 870 chipset is good enough for most (read all) practical purposes. Gkay's right. Look at the firmware side. Try flashing your BIOS, update the drivers and still if the stability issues persist, only then look for a new Mobo.
Even then you wont need a $150 Mobo IMO. An ASRock 870 EXTREME3 should be more than good enough. (16/4 Xfire shouldn't matter anyways 'coz you have an NVidia card)
Mobo should not be the problem, it is a good board. Have you Overclocked or anything to cause the stability issues?
Have you played with RAM settings? These are usually the first cause of stability issues. If the settings are correct haveyou tried using one module at a time?
If it really is a board problem then it is only a defected board and not an issue with the model in general so you would be able to RMA it.
it freezes at seemingly random times, when nothing is really being used, often switching between broswer or steam to desktop...used to be triggerable by plugging in 4 or more usb or multi GPU as well. RMA'd and now it freezes randomly, but not triggerable, so some problems went away.
problems occur at both stock and OC...ram is set to specified timings...cant't remember if I tried bios update, because it won't run my ram at the most recent bios revisions...will try just to make sure....i think it crashes even at stock at latest bios
Currently running one stick at a time to see if it crashes, and it doesn't seem to be, with either stick, but im going to run it for a day or so for each to make sure.
it freezes at seemingly random times, when nothing is really being used, often switching between broswer or steam to desktop...problems occur at both stock and OC...i think it crashes even at stock at latest bios
If it's freezing @ stock, could be a virus / malware problem. Check out the Task Master to see if any weird programs/processes are running that shouldn't be. Also Check out the start-up items from msconfig to see if any weird / unknown / unwanted programs are starting up.
Also set all BIOS settings to default & try to run the system that way for a couple of days. Doesn't sound like an hardware issue. If absolutely nothing else works, before RMA'ing re-format your hard disk & do a clean install. IMO that should take care of the problems if it indeed is a software issue, which I think it might be, especially if all settings are at default.