I also have a Yamaha CM-500 and it works great.
Two suggestions that I have:
1. as for that "third hand", try adding a foot switch to the PTT input on the back of the K3 (search for "foot switch pedal" in eBay or other places). Works GREAT! You may need to make a small adapter to take it from the 1/4" connector on the more common foot switches to an RCA connector.
2. You can easily and quickly switch between the front panel mic connector to the rear panel mic input using the "PF1" and "PF2" buttons by adding the commands:
Macro 1 NAME: MICSELD Command: MN053;DN;MN255;
Macro 2 NAME: MICSELU Command: MN053;UP;MN255;
to your PF1 and PF2 command
Pressing PF1 will switch between "MIC SEL" FP.L to rP.L to LInE In
Pressing PF2 will switch between "MIC SEL" LInE In to rP.L to FP.L
So you can quickly switch between the inputs.
I use the "LInE.In" for my remote input from the computer (RemoteHams.com) so I can switch inputs even if I'm not at home.