The lower bass is so much stronger and so much more detail as well, they just feel alive. I've been listening to music without a sub for the last two weeks and honestly I don't feel like it's needed(movies excluded). .
The Yamaha by itself could play to insanely loud levels without breaking a sweat, but now I can listen at 75-80db and the speakers sing with enough bass to make my hardwood floors vibrate. Before I had to play at much higher db level for the same "sound".
I beleive the newer receivers like the 3808 will prove better than my 5 year old Yamaha though, and the difference between it and a separate amp might be negligable. I have not heard the newer ones though.
That was how I felt with the M80s and the A1400. My Denon 3808, much like your Yamaha, can hit very loud +100db levels but the A1400 just worked soooo much better even at the same low db levels, so no, older/newer receivers are not in the same league as seperate amps, IMO.