I have heard and much admired those speakers. They are fairly balanced and on the warmer side. I don't think they need tubes in the mix unless u like to roll.
I have the older amp version of your INT - 372Bee for the last many years. It is a keeper. I recently swapped it out for a well received 500wpc ICE amp($2K). Could not hear a difference/upgrade! I paid 350 for the NAD 6 yrs ago for a used unit.
What are you looking to do with this change?
I like Brystons personally with any speaker - lots of good deals on SST2s with the cubed out. That said there are many good choices.
Good luck!