FWIW adlelare, I have no crashes at all with JRiver on 1 JR Media Server (Server 2012R2 also running Active Directory and one or more Hyper-V Virtual Machines), 4 HTPC (W8.1pro), 1 desktop (W8.1pro), 1 laptop (W8.1pro) and 1 W8.1 tablet.
I do OTA ATSC television (on 3 HDHR), movies, audio and photo with MC20. MC20 is rock solid for me. BUT all machines are clients of the JR Media Server which is the only one to control the tuners.
However, the big difference and a possible source of trouble for you is the multitude of "media" programs you use, possibly 3 of them competing for TV tuners.
Also, how "fresh" are your Windows installations ? Given the nice Windows "feature" of self corrupting and balooning the registry over time, compounded by possibly multiple installs and removals of software, your issues might be related to that.
A long time ago, I started a tradition of rebuilding my Windows machines once a year, from a clean Ghost image. Served me well !
I do not want to piss you off, but to give you an idea of the developpers task of dealing with a very complex program living in an open and complex ecosystem. Simplification might be your friend !
If you have 3 PCs and 4 laptops, can you afford to start in a simpler fashion ? Start with a clean machine which is the only one accessing the HDHR and verify correct operation. Then make it a JR Media Server and connect a clean JR Media Center client machine. Don't do everything at the same time with unknown state machines !
The issues you have may appear in JRiver but be related to causes external to the program. It is reasonable for the developpers to request crash logs.
Cheers !