Hard to tell exactly. SMSL claims 150W x 150W (2Ω), 90W x 90W (4Ω), and 50W x 50W (8Ω). Converting those figures using RapidTables we end up with:
6W, 7.2W, and 8W. I can't go past 40/70 on the volume knob before it gets way too loud so I'm not sure when audible distortion would kick in.
Just got mine today. I have it paired JDS Atom DAC (RCA) and is an upgrade to my Atom amp. So far no coil whine or noise otherwise. It's cooler to the touch than both Atom parts after about an hour of use.
With the Atom amp, my DT770 pro 80ohm would cause the amp to clip at lower frequencies...