What THX thing?
Your AVR accepts info from Audyssey then makes recommendations based on the AVR manufacturer's point of view, not necessarily Audyssey's. If it was recommended that any speaker be set for "Large," it would probably be best to ignore that. The Audyssey people are dead set against any speaker being set to "Large."
Try using Audyssey FLAT, rather than Audyssey when you play movies or music. You don't need to re-run the calibration, just switch back and forth between Audyssey and Audyssey Flat on the screen. Plain old Audyssey (often the default choice), AKA Audyssey Reference, puts a very slight dip in the midrange, and rolls off the highs a bit. Audyssey FLAT does neither. Using Audyssey Flat should increase the clarity and the midrange.
If you are using DEQ, you may want to try switching it out. Some of us think it can muddy up the sound. If you turn DEQ off, the tone controls become available to you. Unfortunately, they only affect the Front Left and Front Right speakers, but I find them helpful anyway. Most people here turn up their subwoofer a bit. The sub trim in the AVR should be at or below -
5 or the line driver on the AVR's sub output might overload and cause distortion, so for added "punch" turn up the sub at the gain knob that is on the sub itself, and turn up the bass tone control for your LF & RF speakers.
You may have done all of the following already. Try to "toe-in" your Front Left and Front Right speakers a little more so that they are aimed at the center seats, not aimed so nearly straight ahead. Aim the center channel speaker at the center of the seating area, and perhaps tilt it up a little so people can look down the throat of the mid/tweeter horn.
Maximum clarity is most likely when all regular speakers are set for "Small" in the AVR, regardless of what size they really are, and the main crossover for the sub(s) is set for 80 Hz.
Some extra clarity might be had if the LPF for LFE in the AVR is set for 80 rather than the 120 Hz that is usually recommended. I really
didn't want to do this, so I resisted it for a period of years. Since a respected manufacturer of subwoofers, and some people here on the forum recommended it, I tried switching back and forth for a couple of months, and guess what, more clarity in the 80 Hz position!
Check to see if all your speakers are wired for the same polarity ("in phase"). The speaker cable should be marked in some way so you can put + to + and - to - at both
ends of each cable, and have the same polarity for all speakers. If you have a test disk, double check it with that.
they are clearer than any manual since life was simple, technology did not double cross us, and 2 channels were a lot.
Guide to Subwoofer Calibration and Bass Preferences
Audyssey FAQ Linked Here