Do preamps have a material affect on high level sources?

But why then, isn’t it common to drive a power amp with the variable analog output of a good DAC?

There aren’t that many around, most are done in the digital domain.

But if you do have one it’s still fine, what you've got is a passive preamp but it's in the dac, same ratio rules apply. If volume pot is right on the output of a dac, so long as it’s 1:10 or higher ratio to the amp.
EG: volume pot is a 10kohm pot, and the amp it’s feeding input is >25kohm or more input impedance. (A 10kohm pot has a worst case output impedance of 2.5k) 2.5k into 25k there’s your 1:10 impedance ratio.

My Benchmark DAC3 L is directly connected to whatever amp I happen to be running. I also route my Rega RP10/Parasound JC3+ through the analog input to the main amp also.
I have not powered up my preamp since installing the DAC into the system last November.

You know what you do now? Sell the preamp and party.

Cheers George

vjpacor

Dac’s with passive analog volume controls in their outputs, and interconnect interaction, is a bit of a furphy.

Most good quality interconnects are much less than 100pF (picofarad) capacitance per foot.

EG: Say you have average quality cable at 1mt long and 100pf per foot, worst case is 300pf capacitance, this together with the dacs 2.5kohm analog passive volume control, will give you a high frequency roll off still at a staggering 212khz -3db!!!!!!!! Faster than most amps can do.
And if the cable is 2mts long it’s still at a respectable 106khz -3db!!!!!

So as you can see this talk about active preamps being able to control the cables capacitance, is a huge furphy, thought up by active preamp makers to aid in their product sales.

And by going direct, you don't get the coloration's/distortions that active preamps bring, if they didn't they'd all sound the same. Just like going direct!

Cheers George

@georgehifi 
 No surprise that a preamplifier OEM would respond with that rubbish. Pints for the house!!  I will miss the pretty tube glow however.

BTW my interconnect cable is 55 pf per METER, not so hard to overcome even when running 5 ft to mono blocks.

Yes that's fine, good quality ones are lower than 100pF foot.
  
Only if you've crap interconnects with high capacitance and over 4mt, does so called "driving the cable" become an issue As I said it's something manufacturers of active preamps have hung onto just to do scaremongering tactics with.