I have the SB2. I use Coax or Opt out to quality DACS. I compared to Cal Icon II (Power Boss upgrade) and Cal Delta as transports. IDENTICAL, as far as I can tell. As a transport, I could not hear any difference with an upgraded, linear 5V 2a PS. I play 320 KPS LAME CBR almost exclusively. My systems are pretty resolving, including EMP/PPX3 SD650/Cardas and Cal Alpha or EAD Encore as DACS and good tube and SS amps and highly rated speakers and cables. Nice stuff all around.
If these are differences between SB as a server of hi bit MP3s and the original CD they are so subtle that neither my golden-eared son nor I were able to distinguish better than chance. I thought I could hear a difference--but could not when blinded better than 6/10 times. This was SB2 and Cal Icon II into EAD Encore or 24/96 Cal Alpha DAC and switching after listening to a good reference song all the way through, or quick AB. I used three different speaker setups and the EMP with SB and Cal Icon as transport.
While the analog outs on the SB2 are quite decent (like a mid-fi CDP), they do NOT compare to a good DAC ultimately in any way.
I think in the next decade, there will be two types of 'transports': Vinyl and servers. I've sold all my transports keeping only the Cal Delta for tests and just in case.
I assume that upgrades affect the internal DAC/analog sections of the SB--but as a transport alone for a DAC, the SB is fine as is to my ear. However, I have not tried a real (i.e., expensive, modded, boutique) dedicated PS, only compared the stock (switching) to what seems like a nice linear 120V 5V/2a supply that powered a ZipDrive. No difference.
HP out on SB is nothing to write about.