Thanks for posting comments and information about the Marantz chipset, I forgot to mention that my Marantz CD player is the 5001 model
Basically my exercise area stereo rig is my former living room stereo after upgrading there,.... so moved the other stuff downstairs.
The Marantz CDP and Squeezebox feed a Musical Fidelity V-DAC with toslink and coaxial.
The DAC outputs to a Jolida 202 tube amp that has inputs only.
Really don't want to use RCA splitters to go to both the Jolida amp and a stand alone headphone amp, so am using the Matrantz headphone jack for the time being.
I use Audio Technica ATH AD700X cans with a Little Dot MkII+ in my main listening area upstairs. Stock, the Little Dot was fairly close to the Marantz SQ , but after burning in and tube rolling it sounds pretty nice. The 700X's have a better balanced bass and ear pads than the regular 700's but less construction and cable/plug .