I have tried a CJ PV12 (preamp) with an older class D NAD amp, but eventually removed the CJ because it imparted too much hum. Now I use a Chord DAC to drive the amp directly and it sounds good, but not nearly as good as my all tube fully balanced Cary preamp and Atamasphere amps - and I'm driving a 4 ohm speaker with a 16 ohm amp with no problems because I’m also using ZEROboxes. Recently, I added an ISOCLEAN wall outlet and power cords and I’m in heaven! I hear so much more detail and the sound is even more natural. In fact, the signal is so clean I have no overly warm tube sound at all. Amps are plugged directly into the wall and other gear is running on a standard outlet with an ISOCLEAN power strip.
If I'm looking for "Tube Sound", why would I put a Tube Pre in front of a SS amp?
I'm purposefully not specifying speakers as I would like to know in general terms the arguments for and against. So, to the degree that speaker characteristics could also influence the choice, please explain. FWIW, I do not know a phase angle from an impedance curve so I will try and educate myself as we go along. Hopefully, others may benefit too.