Hi! The UR44 is a much better Audio Interface and for what you want to use it for (imo)! I have: UR22, UR44 & UR 824.
The UR44 has 2 headphone inputs (as you wanted). The UR22 has only 1.
The UR44 has MIDI input (might be good if you’re using MIDI keyboards, MIDI whatever…). I dont Think UR22 has MIDI-connection, but it might have it…
The UR44 has more (I Think 4) Inputs/Outputs, so you can connect more (max 4 I Think or even more maybe) devices at the same time. The UR22 has 2 Inputs/outputs, thus you can only connect like 2 instruments at the same time with it (I Believe)…
The UR44 served me well for many Years! It also has “zero latency” technology with in-built dsp effects (Reverb, Guitar Amps, Compressor and EQ) that you can take advantage of (I dont Think the UR22 has that if I remember correctly).
Well that’s about it I Think! Just do your reserach well and you’ll find what fits your needs the best! 
No Point in spending more Money than needed, but I Believe you wont be dissapointed with the UR44!
Regards, Robin Gardner