Krell S-300i and headphone amp

Hi all,

I just received a second hand Krell S-300i integrated (in great shape and sounds amazing).  I want to be able to connect a headphone amp for private listening.  Usually I would use a tape out to feed signal to a headphone amp, but the Krell has no tape outs.  It does have preamp out RCA connections, so I tried connecting the headphone amp to those.  But I don't seem to be getting any signal out of them.  

I'm awaiting an answer from Krell on this, but thought I would ask all of you experienced and clever people as well.

Any ideas what I'm doing wrong, or how to get the desired result?

I guess I was being a bit dense.  I do indeed get signal from the pre out fed to the headphone amp, but not with the volume on the S300-i turned off or muted(duh).  So there doesn't seem to be a way to use the pre-outs for headphone listening with the speakers silent (short of disconnecting them).  Does that sound right to y'all?  Is there any alternative?

Does your headphone amp have a line out?  You connect your source (turntable or CD player or whatever) to the headphone amp's inputs and the line out goes to one of your inputs on the Krell.
Thanks Greg (or is it Big?)  
No, the headphone amp in question has no line out.  I suppose I could get another one that does, but what with the length of IC cable I'd have to run to make the application I am after work, it is probably not worth it.  The Krell is so forward looking in other ways -- iPod hook-up, HT pass through, etc. -- that it's a bit surprising their designers didn't foresee the headphone craze and add a tape out or equivalent.