Help Me Improve My Turntable Set-Up

I agree that the Schiit setup is probably holding you back a bit, if you're in a room bigger than a small office. But could there also be an expectation gap here? In one of my systems, I have ProAc Tab 10s, which are close in specs to Harbeth, and I expected the world when I bought them. And they are amazing - super clean, articulate, can hit volumes...but they simply can't produce that depth that allows you to be enveloped by the music. I still love em and have come to terms with their character. I have vintage DLK 1 1/2 in another system for a fraction of the price and the music is "alive". Size does matter.

The Saga+ has no gain. The Aegir has an input sensitivity of 1.2V, but the Mani output should be about 300mV for a standard MM cartridge. It’s not a big surprise that you aren’t getting much life out of the Aegir. Even with low efficiency speakers it should do okay unless you’re asking for high volume. The dual mono Aegirs might help since you’ll need to go balanced to do it, and most likely use a pre with gain.

i’ve run the Saga/Aegir into 87dB floorstanders and filled a big open room to respectable volume with aplomb. However my DAC outputs 2V.

I think you have to try to find some opportunity to listen to someone's system that sounds the way you want yours to sound and work from there.  It sounds like you're just generally unsatisfied and you're guessing at what it might be.  Unless you know what you are trying to achieve, it's impossible for anyone to make suggestions, no matter how well-meaning. I have the Harbeth P3s as well and I would describe the sound as very natural and realistic for their size. With the right recordings, they can sound like live music, but I think that's not what you mean when you say "come alive".  

Are you analog only? If there is a dac too do you feel the same re shortcomings from both formats?

I agree Harbeths are tough on amps ( which is not a great trait for a loudspeaker imho ) although they can sound nice.

Schiit gear is decent for the money but nothing more. Give your super expensive book shelves a better amplifier.