New here, but headphones are a familiar (in fact, obsessive) topic to me. In my home office I have two separate audio systems, each with its own computer as source (via USB cable) to a DDC feeding a DAC:
Main system: The DDC is a Matrix Audio X-SPDIF 3. The DAC is the MHDT Labs Orchid, which I paid to have modified by addition of a 2nd RCA output pair on the back panel. From the DAC signal goes to two headphone amps, one of which is a preamp (I change these fairly often). Currently these are the Wells Milo & Violectric V281. The preamp output goes to a Marchand electronic crossover which feeds high-pass signal to a Wyred 4 Sound ST-500 class D amp, which powers a vintage pair of KEF 103.2 two-way speakers; and the low-pass signal goes to a JLAudio e110 subwoofer.
Side system (headphones only): The DDC is a Matrix Audio X-SPDIF 2. The DAC is the Metrum Onyx, each output of which goes to a headphone amp (currrently the Icon Audio HP8 TC-tube amp; and the Cavalli Liquid Carbon v2).
Of course there are other pairs of speakers to rotate in and out of the main system: ATC SCM12 Pro's and a pair of Harbeth 30.1s just purchased from the UK. There are also multiple pairs of headphones. These range from the modest/affordable (Marantz MPH-2s; Philips Fidelio X2s); to higher end models (ZMF Aeolus; ZMF Verite Open; ZMF Ori; Final D8000).