Air Tight ATM-300R or Shindo Cortese 300B

If you are looking for something ultra musical and very traditional sounding for a 300B, check out the Art Audio Diavolo.  It is supremely well designed and is a popular choice in Europe.  Aesthetically, I think it is very good looking and build quality is first rate.  My biggest issue as the US importer is that these amps never die.  I regularly talk to people who are in year 15 or 20 of ownership and looking at a refurbish, rather than replace.  

Your preamp is well suited to the Diavolo with 1v of output and you will get the lush, musical mid-range that people crave from a 300B.  

Air Tight and Shindo are undeniably brilliant.  I think your comments above are spot on regarding these two brands.  Shindo would be the better choice based on your description but I also agree that Shindo is best with all Shindo.  

Good luck.  

Wow, that is miserable.  I wish you luck in terms of finding the right amp.  Good news is Shindo and Air Tight are not average amps and you aren't settling with either of them.  

Have you thought about the Luxman?  It is phenomenal and ships with Takasuki's?

I am certain Tom will ship directly to you from the UK or I could arrange for delivery to you as I am always happy to help the brand globally.  
If you were merely being polite, cheers and good luck.  Understand completely.