Hi,
Before you try KT120s, read up on the Tung Sol 7581A. There's a slight dip in power but has a really balanced presentation with a tad more bass presence and upper end air over the EL34. I have them in my Evo 400 and really love the extra bit of detail. And they're inexpensive.
Do try the low output MCs, even if to compare against your HO MCs.
That particular McIntosh phono preamp is a good jack of all trades. I've found that going to a dedicated MC phono preamp was a better path for me. I use a Hagerman Trumpet MC and it does an amazing job getting my AT33PTGII cartridge to sing with no noise.
I can match any MC cart with the affordable, all-tube Hagerman.
Good luck!