I have a ZMA and I keep my ZP3-Turntable connected to the RCA and my DAC connected to the XLR all the time with no negative impact. I just don't use them both at the same time.

Well, I'll post my results here in case others want to do the same.  Got the amp.  Sounds great.  Awesome balanced inputs with transformers.  

Steve filled up every square inch of the top of that amp with components:  4 transformers, 10 tubes, 4 gauges, 4 bias adjust pots, etc.  So I'm having trouble finding a place to put a switch.  I've given up on rotary switch and since there are only 2 sets of inputs, I'm going to try to find a place to shoehorn in a toggle switch someplace where it doesn't look crowded... gotta take the top off and look at it from both sides.  Manual says it can take up to 8 hours for the big caps to discharge.   I'm also toying with the idea of putting a switched resistor across the caps so I can flip a switch and dicharge them in 60 seconds...tube rolling is a bit more challenging if you have to wait 8 hours to switch tubes.

More to follow.
Jerry

Thanks Archie. I tried this.  It only played a few seconds, similar to what I'm used to other amps playing down that don't have large caps.  Makes me think they probably didn't discharge so be careful.

Your experince swapping output tubes confirms my thought that it is really just the OA3s you have to worry about.

thanks for this.
Jerry

UPDATE:   Yesterday I installed the selector switch with great success.  I have to say that my main DAC is loaned out right now but with my backup DAC I am super happy with the sound.  

While I was in there I replaced the signal cables (from inputs to volume knob, to input tubes) with Mundorf Copper Angelique 18 awg solid.  (proprietary blend of Cu, Ag, and Au).  

I am very happy with the sound.  I was finding the XLR inputs a bit harsh and had been listening to the RCA.  Now both sound great and harshness is gone.  

The install was very clean.  I put a small DPDT switch just in front of the output transformers.  I was going to use SPST but decided to switch the ground too.  The original wiring grounds to the chassis but the signal cable is shielded and the shield in grounded on both ends.  I didn't want to change anything so I ran a ground wire to replace the shield wire and switched it too.    

I also installed KLEI RCA inputs as I am a believer in low mass.  I'm going to make a set of interconnects with the matching connectors but used more wire than I expected and don't have enough wire left over to make the interconnects.

Here is a photo showing the small switch and the new RCA connector (sorry, should have unplugged the connector).  https://share.icloud.com/photos/0ec-qDHCADnauN2FRMsHCvvtw