Thanks for your input. My main concern is that I am not getting all that I could out of my AKG 702's or that I would not have enough power for the Sennheiser 650's. I have never used a headphone amp before, so not really sure what the difference would be.
I agree, there is a fair amount of power that is sent out from the output controls in the SP40. What confused me a little is that Focusrite posted a kind of apology that their headphone amps aren't that strong, because they wanted to avoid clipping at all costs.
Originally Posted by DonM
I use my SP40 and Sennheiser 580's every day. I also use my classic 414's that I'm pretty sure are 2k ohms - the SP40 drives them fine.
Since you can create a mix just for 7/8 9/10 that is dedicated to the Headphone outputs you have a lot of control regarding levels.
What are your specific concerns about needing the amp?