Dumb question? Issue with hooking up either a DAC or preamp to two different "systems?"

@almarg. Thanks.  Those were the two potential issues I thought of, but wasn't sure if the input impedance of the two connected items would get coupled or if there is a difference if one item was turned off.  And the potential for hum/noise since there would be more "stuff" connected.  If there should be no harm, though, (e.g., blowing something up), I'll give it a shot.

@2psyop .  Thanks. I've tried things both ways, too, in different configurations.  Sometimes and sometimes music-dependent, taking out the preamp or using a passive seemed better.  Sometimes not.  I did completely separate theater and stereo.  Completely agree with you there, even with pass-throughs and such.  Theater is less than 10%, though.

@kalali.  "The only issue I ran into was my hybrid amplifier has a tube input stage design that shorts the inputs when the unit is off..."  Thanks.  What happened?  Noise, no sound, smoke signals?

I've done the same with a Bluesound.  No issues so far connecting the digital to one system and the analog RCA to another.  Great, versatile, items, imo, especially for the money.

I ran my two systems using the same preamp before I got a separate preamp. The only issue I ran into was my hybrid amplifier has a tube input stage design that shorts the inputs when the unit is off so I always had to turn this amplifier on regardless of which system I wanted to use. Other than that I could not tell if the sharing affected the sonics in a bad way. I still have my Bluesound Node2 feeding both systems, digital output through an external DAC to one system and the analog output going to the other. No difference in the sound quality if/when I only use one output. 

I would not do it. I have heard of people using home theater equipment with (double duty) stereo equipment. To me mixing and matching unlike equipment or for unlike purposes complicates the system. Keeping things simple always sounded the best to me.
Once I had a stereo amp, preamp, DAC, and CD player as a single source system. I took the preamp out of the system and it sounded better, because my DAC could act as a preamp.

There would be no harm in doing that, Stfoth, although the resulting sonics **might** not be quite as good as they would be if only one of the outputs of the preamp or DAC is connected.

It is not uncommon for preamp and DAC designs which provide both XLR and RCA outputs to drive both outputs with the same output stage, with the signal provided to the RCA connector being the same signal that is provided to one of the two signal pins on the XLR connector. In that situation the possibility of impedance-related sonic issues is increased, even if one of the amps or other destination components is turned off, since two load impedances would be presented to the same signal.

Hum or noise issues could conceivably also arise, again even if one of the two amps is not turned on.

But it all could very well work out fine, depending on the specific designs, and there’s no harm in giving it a try. And of course it would be easy to determine if there are any adverse sonic effects, by simply comparing sonics with the output that isn’t being listened to connected vs. disconnected.

Best regards,
-- Al