Schultz9927t wrote:The Shure SE-215cl’s are rated an impedance of 17 ohms thus leading me to think that amplification is not need to drive them.
I have no idea why you're led to think that... but you're completely wrong! A headphone amplifier is most definitely required.
The specs for the HP2 are a little odd...
They quote a max input level of +4dBV which is only +6dBu... although the input actually limits at +5dBu (see below), so getting the gain structuring right from your console will be important as it will be very easy to overload the amp inputs if you're not careful.
Oddly... having defined the max input level in terms of dBV, Presonsus bizarrely choose to describe the input limit level in terms of dBm. However, dBm is only a relevant term in this context if the input impedance is 600 Ohms, but it's actually 15kOhms... so someone has got themselves in quite a muddle somewhere.
Moving on, the output power is quoted as 50mW per channel with a 20 Ohm load, and that's fine as your Shures are close to that at 17 Ohms -- which is also comfortably above the 12 Ohm minimum impedance* for the amp. So there's no impedance issue to worry about.... *except that I see in the user manual they state the minimum impedance is 16 Ohms and it is possible that the Shures dip below that at some frequencies. I'd be surprised if that is the cause of any problems, though.
The sensitivity of the Shure SE-215CL is pretty high at 107dB/mW, which means with the HP2 amp running flat out you should be able to generate around 123dB SPL into the performers' ears which ought to be more than loud enough... That is the notional threshold of pain, after all!
So I suspect any distortion you're getting is most probably due to over-driving the headphone amp inputs, rather than mismatching between earphone and amp.
If users are complaining that it's not going loud enough, check their earpieces for wax blockages and that they're fitting the earpieces correctly.