This is for Georgehifi especially but others can chime in.

passive preamps commonly suffer from their own problems that can easily affect the sound,

Rarely, not commonly, around 10% of the time there can be mismatched impedance's when the source has tube output stage which is too high in output impedance, or it's output coupling cap is too small, which will  give a very high output impedance at low frequencies.

These types of sources direct, would be also mismatch into many Class-D amps as well, as many are 10-20kohms input impedance, just like a passive.

Cheers George 

bubba 12
I have the Pass XP12 running through a pair of AVM 3.2 Mono's (which are D class) I tried the Pass XA 25 with my Dyn C1 Plat.
They just like more power... I also use a comet dac with this set up
I am not pushing D class but it does work well with the system
I am sure there are a number of power amps that will do a nice job
good luck with your search
Dennis

Can we clear something up? All passives basically suck. It's unavoidable. Let's not confuse passives with buffers just because the stage isn't making gain. If it's got active devices, it's an active pre-amp. 

All passives basically suck.

Your First Watt amps have very little or no gain, I can see this maybe your reason behind this statement.
But that’s your opinion, and you are entitled to it.
It is a totally incorrect statement if there is no impedance mismatch or gain problems as First Watt amps will have, there is only transparency, dynamics, and distortion advantages over any active/buffered preamp with or without gain.

As quoted by Nelson Pass:
" What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection."

Cheers George

@dsremer  I will be getting 260.8 monos from Pass Labs or 60.8. The XA 25 is not enough juice. I agree. I will have plebty with monos. I am going to stick with the XP 12 preamp. I’m enjoying all the suggestions and interesting asides on this thread.Thankyou everybody.