The SUBPAC S2/M2 models are rated for headphones rated from 32 ohms and below.
If you are using a SUBPAC S2/M2 with headphones that require more than 32ohms (most headphones are under this limit), you will get the best performance by using a matching high impedance amplifier separate from your SUBPAC.
If you want to use your high impedance headphones connected directly to the SUBPAC, be sure that you do not clip or overdrive your SUBPAC while driving your headphones up to a comfortable level.
Please contact our customer service team directly if you need more assistance with using high impedance headphones.