When you connect headphones to the front of the Icon HD, the device acts as a Headphone Amp. When you unplug the headphones an internal switch engages the RCA Line level outputs on the back, which you would then connect to an amplifier for powering speakers. :)

Why not give it a try. There is a 30 day return policy if you don't like it. :) Here is one review.....   https://www.evernote.com/pub/nuforce-marketing/amplifierreview#b=0d378b99-78fc-46dc-949e-f273b8668f47&n=c889fcd4-102a-4cb5-8af2-43c765d963e7

The only way to connect to the uDac-2 is by means of  USB connection from a computer. Then you can either use the internal DAC/Headphone amp, or use the S/PDIF OUT to connect to a different device with a S/PDIF input bypassing the internal DAC/AMP combo. In this regard it is strictly a USB to...

Are you sure you are changing the OUTPUT and not the INPUT sample rate ?

The guidelines for system settings are intended to assist you in the setup and operation of your Nuforce 24bit/96kHz USB DAC products (Icon HDP, uDAC-2, uDAC2-HP, Icon2 etc). USB is good only to 24bit/96kHz any higher resolutions must use the coax or optical SPDIF.   Best Regards, JasonS

The optical input of the HDP works up to 192kHz, but MANY OTHER PARTS of optical, such as the cable and the source DON'T SUPPORT > 96kHz. The HDP supports 88.2 and 176.4 but not via USB.   Hope this helps, JasonS