Tube Pre-amp or Buffer between Tape Monitor

I understand some people use a tube buffer or tube preamp between the tape monitor feature of their ss gear to achieve a warmer sound with the ability to switch it off via tape monitor.

I was wondering if anyone has tried this and what results were gained or lossed. I am thinking of acquiring a Woo Audio HP preamp again to try so that I will have not only the ability to listen with and w/out the tubes in the circuit as well as have a nice headphone amp.
I haven't tried it, but switching a tube circuit in and out of the main preamp circuit (essentially as a signal processor) in this manner sounds like a perfectly viable thing to do. What it sounds like would depend on the specific tube circuit and interconnects utilized more so than the approach itself, I would expect.