Anybody hv a recomendation for a good suitable headphone.
As others have mentioned, find something with impedance higher then 200 ohms, then you're sure the Crack can drive them with plenty of headroom and control.
Choice would be down to your preferences sonically.
I have tried my Crack+SB with following headphones: Sennheiser HD650; Beyer DT990 (lightly modded) and Beyer T1 2nd gen.
My DT990's are modded a bit with extra damping of the driver to take the "edge" of the normally quite hot/sibilant treble. But otherwise a great can if you like extra emphasis on the low end and treble. After around 15 years of use finally teamed by my T1 2nd gens.
HD650: They just sing with the Crack! Sound is to the "cozy" side, but very pleasing and musical. Personally I get a tiny bit bored though
T1 2nd gen: Beyer house sound again. If you can enjoy a bit of excess energy in the treble, then it's just a no-brainer to me. So entertaining presentation and details are presented so precisely. Very neutral bass presentation that extends all the way down.
I was very close to ordering a set of Beyer DT1990 Pro's but ended with the T1's. But I would urge you to check reviews of them. Seems tempting.