Best speakers for LTA Z40+ Integrated amplifier

I'd try what you have first you may find it works fine. 

I have Magico A3's they dip to 3.8ohms at 88db and I tryed a 30wpc SS amp on them for fun, and i'm still using it from time to time as its sounds wonderful. Will it blast at 100db, no but i don't listen at those levels, I like my hearing. But at 75-85db its great. 

I agree. I am researching possibilities to squeeze the best performance out of the Z40+.  I may be perfectly happy at reaching my goal with the ATC's in my home office setting.  But I'm further driven by the knowledge that when my daughter graduates from high school (couple of years) I will sell our home and its dedicated listening room.  I'll have to dismantle that system and intend to replace it with the Z40+ as core amplification, thus the survey. 

I had the LTA Z40+ and I used it with Spatial Audio Labs open baffle speakers (the X5s). Spatial Audio now has a new set of speakers but I’m sure they would match well and Spatial Audio used to use LTA to demonstrate their speakers at shows. I also used the LTA with my Nola Boxer S3 speakers. 

I must mention that I replaced the LTA with Don Sachs’ Valhalla integrated tube amp which was significantly better in almost every way over the Z40+. Additionally, I had to upgrade the stock preamp tubes from the LTA after I bought it. This was before the Ray Tubes was offered as an upgrade from LTA. If buying the LTA now, I would definitely upgrade to the Ray Tubes which are great sounding tubes in my opinion.