The last week I've been playing with the Focusrite Scarlett 2i2. I noticed that to get this audio device loud enough to power my Sennheiser HD650 300ohm headphones to full volume, I had to turn up the volume of the piano in the Pianoteq interface. I started to notice some distortion that made me think that I would need a headphone amp to go with this.
I had time today to compare the Scarlett 2i2 to the Behringer Q502USB using Pianoteq. The Scarlett is only USB powered. The Behringer unit is AC powered and makes the headphones much, much louder.
Still I noticed that both sound cards sounded better when I played Pianoteq with my much cheaper Audio Technica ATH-MS50 headphones. This surprised me, because when I had A/B'd these headphones months ago with a pricey Sound Blaster PCI audio interface that had a dedicated headphone amplifier, the Sennheiser's came out on top.
So Njaremko is right. a 300Ohm headphone needs a headphone amp.
Using the Audio Technica headphones, I compared the Focusrite Scarlett 2i2 to the Behringer Q502USB. I noticed absolutely no difference in any range of the piano. The Behringer is listed as a 16 bit interface, but in ASIO4ALL, it says 32 bit while the Scarlett says 24 bit. No matter. I could not hear a single difference between these two interfaces after an hour of A/B'ing.
Only one thing, when direct monitoring is turned on in the Scarlett 2i2, there is a light hiss regardless of there being a signal. The Behringer is super quiet when I have my smart phone headphone jack plugged in.
So the Behringer gets the edge. I'm going to look for some lower impedance headphones to replace the Audio Technica's. They sound great, but they squeeze my head.
Pianoteq 6 Std, Bluthner, Model B, Grotian, YC5, Hohner, Kremsegg #1, Electric Pianos. Roland FP-90, Windows 10 quad core, Xenyx Q802USB, Yamaha HS8 monitors, Audio Technica
ATH-M50x headphones.