That depends on the speakers (how much current they draw) and the level of the input source. On my system clipping seems to set in around 70-75, so if that's typical then you may be hearing clipping. It's also (on my system) almost unbearably loud, but my speakers are more sensitive.

I'd suggest that the 8db you'd gain from the 755 is more than the 2db from the upgraded speakers, but the upgraded speakers might buy you other factors as well, such as improved voicing.

Also, I don't see any mention of a subwoofer. Without a sub the 1050 is going to route all bass and LFE to the front mains (IIRC) so this will be a factor. Just buying a powered sub may free up enough headroom to satisfy you and will also provide that 'big sub HT bang'. I'd strongly recommend a good sub if you in fact don't have one.

My 1050 runs hot too - I wonder if the amp section is biased a bit heavy into class 'A' or something on this design.