Schiit Freya+ or Saga+? Vidar or Aegir?

I have a Saga+ with an Aegir. If your source outputs at least 1.2V then unity gain with the pre will get full power out of the Aegir which should be fine with your speakers. The Freya+ may be better (I haven’t heard it), but for the price the Saga+ is surprisingly good. As an added bonus with the single 6SN7 it can be a lot less expensive to experiment with tube rolling. 

I’m using Zu Omen DW rated 97dB

I’m have an NOS tube in now and there is more of a difference, but with the stock tube the passive really was pretty close. That isn’t necessarily a bad thing. I have issues with any kind of increased noise floor and am still new to tubes so I was worried about that initially. The major difference would be the output impedance. In the passive mode output impedance can be up to 4.8kohm. The tube mode is only 180 ohms. So it depends on your amp. The Aegir and Vidar are both only 22kohm input impedance, so a passive probably wouldn’t be a good match, especially at low volumes. I had the Saga+ first to use with a new tube power amp instead of using the pre out of my old SS integrated. Playing around with it I actually preferred the sound of the Saga+ both into the tube amp as well as into the integrated. I just left the volume on the integrated to be close to the same gain as the tube amp so I didn’t get any surprises when switching. There is just a subtle sparkle that I enjoy more with the Saga+ in the circuit. I bought the Aegir to get an idea of what a Class A SS might sound like without spending big bucks yet. I’m in an accumulate equipment and experiment phase, exploring what is there with the intention of eventually having a main and secondary system. I have no doubt I’ll eventually upgrade from the Saga+, but I can’t point to anything it’s doing wrong. It was supposed to be a short term solution, but I’m in no rush to pick a replacement without learning a lot more about what I’m looking for.

From the comparisons I’ve read I got the impression that the Aegir is hands down better if you don’t need more power. I’ve also heard they sound even better run as monoblocks. (In which case you can’t use the Saga because you need XLR to run in mono) I never even considered the Vidar for my setup. 

Most digital sources - anything with a DAC - run 2V peak out. Typical phono pre out is 300mV peak (I’m not a turntable person, so I could be wrong)
Look up the specs on your sources. Saga works for me because I’m only running digital.