We have contributed to each other's posts in the past, and this combination is one I know something about having owned several pairs of Klipsch speakers along with a variety of McIntosh tube and SS gear.
Comments regarding the less-than-desirable combination of solid state amplification with classic Klipsch speakers are essentially correct. Presuming that your son has a pair of the (very) large Klipschhorn floor-standing speakers, they were designed back when 25 watts of amplifier power was substantial. Accordingly and as stated by others, they are an extremely efficient configuration that can easily overwhelm many environments as well as much program nuance.
Solid state amps, even those in modest receivers of the late 60s, generally provide more power than that albeit with notable artifacts. I'll leave it to others to argue about what those could mean in your son's world, but to me that means a blunt projection of sound rather than a faithful presentation of it.
An alternative power consideration for a Mc fan in this case might be the MC240 mentioned previously or the (perhaps more readily available) MC275. Both will deliver enough SPL with Klipschorns to make your son's ears bleed, and will do so faithfully to the source material. What your son's neighbors may think is another matter as both will be loud indeed.
Further, a tube pre-amp could also be called-for. You didn't mention what your son has there, but the modern C2500 through C2700 have good DACs and will support just about any vinyl rig available, if that's his flavor. Both amp and preamp are within the budget if he shops carefully and liquidates the MC7300.
Classic Klipsch designs like the Heresy, Cornwall, La Scala and Klipschorn were all magnificent concepts intended to be driven by tube power of 100 WPC or less. Altec-Lansing and JBL started from a similar place. Honoring that legacy would be appropriate. Your son and others may disagree, but starting from a known reference is a great way to create happy listening in my experience.
My very best wishes to your son on his journey!