Total newbie question re: headphone amps

Um, so can you hook up a headphone amp to the tape out on your preamp section of your integrated?

Sure, assuming your tape amp has an attenuator. Most do.
What about a tube headphone amp, fed by the tape out of a Naim Nait 3. My reasons are: I want to try tubes in some way; the Nait has no headphone jack; the Nait has my only phono pre.

Would I get tube pleasure?
My editing was poor. I meant 'headphone amp' not 'tape amp'.

If you are connecting a tube headphone amp to the tape out of your Naim, and your tube headphone amp has a volume control, you should get the full benefit and pleasure of tubes. The only thing that you might want to check out, if you are considering a purchase, is making sure you have a good impedence match between your tape out and headphone amp in and that the headphone amp can drive your particular brand of headphones. I can't imagine that would be a problem, but its worth checking out just to be sure.
I have connected the RCA "tape out" from my pre-pro to my Antique Sound Lab headphone amp (tube) and then to my Sennheisers. Works great! Ask Tosh at ASL about your unit to make sure the impedance matches. He is very helpful. Good luck!