ATC SCM 40 mk2 vs Salk Song3 Encore

I have not heard Salks, though I look forward to doing so one day given the amount of love they receive in this forum

As for ATC’s - I still have 2 pair of their active models... they are spectacularly accurate monitors in the truest sense... what goes in comes out, pretty much exactly... no euphonic sweetning, no expansion of mid bass to warm things up... these are British speakers but imo they are the antithesis of the Harbeth/Spendor school where tonal loveliness and dimensionality and fullness is created by the lossy enclosure and driver design that warms things up ever so slightly (to wonderful effect)... the strength of Harbeths often mentioned is that they make poor recordings more listenable... ATC’s do NOT do that.

You need to match source and electronics carefully with ATC’s ... poor signal in can often lead to shrill or grainy output...

Have fun good luck

Would a Musical Fidelity A308 bring them a clear and strong enough signal? And I use Deezer CD quality through a $400 dac.

I meant to mention it earlier to you tgat the ATC’s are power hungry but your amp should be fine.  I drove ghe Atc Scm7 v2 to satisfying volume levels with slightly less power than you.  I would have ket the scm7’s but they just didn’t have enough bass with that small driver.

either way you’ll want to upgrade your dac.  A used schiit bifrost multibit can be had for $500 or a schiit gungir multibit, like what I have, can be had for $800.  
Those Atc Scm 40 v2’s at $3500 is a pretty dang good deal!