TOPIC:

I am also thinking of adding SHD Studio “upstream” for my SMSL DAC+Amp but the connectivity diagram concerns me. My use is Roon plus audio from Apple TV. 

1. Do I really need a second DAC for just the sub?

2. Will this present a problem:

SHD Studio -> SMSL DAC -> SMSL Amp -> Stereo speakers (no crossover)  + SVS Subwoofer (with crossover)

3. Will SHD serve my setup better? This way I can return/sell my SMSL DAC. 

4. Does SHD studio have “profiles” feature, eg one for music and another for movies? 

5. My SMSL DAC supports MQA decoding and rendering but is it correct that Roon will take over when SHD Studio is used? 

1. For optimal subwoofer integration you'd want to use the SHD Studio for volume control and source selection, and then a line level connection via a second DAC to your subwoofer. This setup means you can apply crossover filters and time delays to your main speakers as well as subwoofer but you'd need to get familiar with making measurements using REW to figure out what is best to use.
2. This arrangement won't allow you to apply separate crossover filters and time delays to your main speakers and subwoofer. It would 'work' but wouldn't be optimal.
3. It would remove the need for a second DAC, yes. Or you could use a fairly cheap DAC for your sub I'd have thought.
4. You can define your own presets for different things like your music and movie examples, but there are no pre-programmed options like this to choose if this is what you had in mind.
5. The SHD cannot do any MQA decoding and the internal sample rate is 96 kHz. I know nothing about Roon though.