rewiring preamp will it work

Thanks, Mingles. That could very conceivably help the situation. The question for Cary then, simply put, is what is the minimum load impedance they recommend for use with the preamp.

Regards,
-- Al

Adding a switch to choose between the two outputs would cure the impedance problems. Of course, anything added to the circuit (wire + switch) may degrade the sound ever so slightly. Probably less compromise than an unpredictable impedance mismatch however.

Your headphones' impedance could be too low even all by itself. Many headphones have impedances like speakers', in the 4 to 16 ohm range. (Putting a high impedance amp in parallel to a pair of headphones would not make a lot of difference.)

Presumably, you would unplug the headphones while listening through your speakers, so the preamp should be OK then. But when listening through the headphones, the low impedance of the headphones could result in damanding more current from your preamp than it can supply without distortion, as others have already aluded.

So, why don't you plug your headphones into the output of your amp instead?

James is correct, aside perhaps from the last sentence, but I and I suspect most of the others have been assuming that the second RCA output would go to the input of a headphone amplifier (as I mentioned), rather than to headphones directly.

A preamp having a nominal output impedance of 560 ohms will be unable to directly drive nearly all conventionally designed headphones, with any semblance of good results.

As far as connection to the amp output is concerned, without knowing the specs of the components that would be involved I suspect that you would be putting way too much signal into the phones unless the volume control is set extremely close to the bottom of its range.

Regards,
-- Al

Very informative reply Al, greatly appreciated. When I plug in the input impedances of my amp and and headphone amp to the equation I get 13.5k ohms for the combined input impedance. So its definitely more than 10x the listed 560 ohm output impedance of the preamp, but not if in fact sometimes increase to 2-3k as you mentioned. What do you think?