I don't have 400's, but I still have a set of TF-700's that I use in an extra room. I run them with a Peachtree Decco and Squeezebox Touch and they still run fine. I was the original buyer, back in 1980'ish and they still sound amazing for what they are. The drivers seem to have held up very well for their age. I have also tried running them off of a McCormack DNA-225 I own and they also do well with that.
Good luck and happy listening....
Rootman
Good luck and happy listening....
Rootman