In response to your question and If I may give you my advice, don’t fall into the trap of taking reviews, comparisons and hype as fact. Specs can give you a reference but definitely don’t rely on them to tell you how musical any component is going to sound. I think you’ve already answered your own question regarding Shiit. I will say that the 3 components that I did try from them were their so-called top of their line and all 3 had issues and got sent back, after I had to deal with what seemed like endless back and forth arguments spanning several days with one of the worst customer services that I have ever experienced. You are comparing apples to oranges. My analogy between Schiit and Ps Audio is like comparing Ford to Mercedes.
I haven’t listened to the Stellar Gold yet, but do have the Stellar Gain Cell DAC/ preamp combo connected to the M700s and that sound is what I briefly described to you. I am sure that the Gold preamp won't disappoint you, but you aren’t going to get the full performance of it with your current Schiit DAC.
I jumped from the Stellar to their BHK series. I bought the BHK components before the Stellar gold came out. The Gold was released recently. If you are leaning toward the M700’s with the Stellar Gold preamp I’d plan on a new DAC also, but if I was in your shoes with your current assumed budget, I would get the M700s new and a used Stellar gain cell DAC/ preamp. Unfortunately, the Gain Cell DACs are sold out new. They will not disappoint, and you have 30 days no questions asked refunds. You do pay the return shipping though.