Preamp/Headphone Question

Hi all,

While I don't consider myself to be a newcomer to the world of Hi-Fi, I am definitely new to the world of "Head-Fi", as I'm being forced into the game for practical "noise pollution" reasons (aka the wife). I'm just wondering what the best way to integrate a pair of headphones into a preexisting (primarily tube) hi-fi setup would be. My Hi-Fi consists of Thorens 160, ARC Sp9 mkII, Dyna ST70, and so on. I'm looking into some headphone amps, mainly the Grado RA-1 which as I understand can be plugged into the tape out of my SP9, making use of the SP9's phono stage. I'm not sure this is the best move, though. I'd like to preserve the tube nature of my setup, but none of the tube headphone amps seem to stick out. Anyone have any advice?
What headphones will you be using and what is your budget for a tube headphone amp?
The RSA B52 is an outstanding tube headphone amp. Expensive, but worth it. It transforms ordinary headphones into great ones.
(Upgraded tubes help, though).
Check out the praise on headphone forum sites.
To be honest, I'd like to spend as little as possible. If it wasn't clear in my first post, I'm being forced into this game a little begrudgingly and would hate to spend huge amounts of money on a headphone rig knowing full well what that kind of improvements I could be doing to my hi-fi setup with that kind of money (if you look at what I have, everything is fairly "budget"). That being said, I can still be convinced otherwise.

I've been lent a pair of Grado SR-125s, and while I understand these are among the low-end of the Grado line, I've been thoroughly impressed by their value (hence the interest in RA-1). I may go for another model, but I understand the range of Grado headphones posses similar characteristics.

On another note, what's stopping me from simply using an RCA-to-headphone adapter and plugging my headphones into the line out of my SP-9? I understand this isn't exactly 'ideal' and there may be impedance issues, but if it isn't 'unsafe' for my SP-9 (I'm not sure if it is), could I potentially eliminate the need for a headphone amp? BTW, I tried this BRIEFLY with a cheap adapter and it sounded acceptable, but again, I'm not sure if this is safe. Perhaps if I invested in a audiophile grade adapter could this work?

Thanks for your input! I will definitely check out the RSA... I've just signed up for a head-fi account.