I have a X4000 (currently in closet as a backup) that I used for 4ish years. It was connected to 2 different speaker setups (both low and high sensitivity) in 2 different rooms both with limited and very good ventilation . My speakers were always set to small with an 80hz for front and 80-100hz for rears depending on the speakers. Audyssey was always used . I listened at -25 to -15 for movies.
My X4000 ALWAYS ran hot and would quite often go into protect mode regardless of which speakers I was using or with limited to good ventilation.
Running a small fan did help but did not solve the issue for me. My solution was to buy an external amp which did solve the heat problem and I never had a shutdown again.
I have used Onkyo, Integra, Denon, Sony and Marantz receivers in the past from entry level to upper range. The X4000 and the Integra were the only receivers I could get to shutdown without actually trying to. The X4000 was the replacement for the Integra so I was not exactly a happy camper with the new receiver in that regard.