@dasherma - You can set the volume control where it is a non issue. I run my DAC through a preamplifier and have set the volume on the Morpheus to a level that works well with my preamp volume and in the Morpheus settings have the volume control on Fixed Volume.
The are some very good reviews of the Morpheus on the web with Stereophile being one of them.
I can't comment on the USB input that you mentioned as preferred as I run my streamer through the DAC with an AES cable. With that said I was just throwing the Morpheus out as a suggestion but I am sure the Onyx sounds every bit as good.