TOPIC:

Hello. I am considering adding Flex/Digital to my system, so that it could drive two external DACs. However, I'm not sure if the volume control of Flex/Digital would work, if external DACs do not have volume control themselves? My setup is LXmini active speakers, connected to Marantz 5-channel power amp (4 channels driving each speaker driver separately). Right now I'm using 2x4 HD, connected to MacBook Pro via USB. I control the volume from the computer. Considering that 2x4 HD has a mediocre DAC, with Flex/Digital I would aim to retain the 4-channel processing to output the signal to two external higher-quality DACs (eg. two Topping D10, D50 or similar). Just how to control the volume? Will Flex/Digital volume control still work, or should I actually add volume-controlled DACs and try to match their volume levels (and control them combined, somehow...).

You're way over-thinking this. 
The digital volume control in the Flex is perfectly fine to use as your system volume control.

Dave.

Thanks. But do I still need two DACs? Is there a DAC model that accepts two inputs simultaneously?

Correct, it would control both DAC and they would be in synch. 
As for a QUAD DAC with Dual SPDIF/TOSLINK input, not too common.  

You can always grab a Flex TRS/RCA. See the specs. These are a lot better performance than 2x4HD. 

DevTeam