["Rotel is a great brand and their receivers won't disappoint you, but are you looking for better features or better sound than your Onkyo TX-DS676?"]
Better sound.
["but the sound quality is not likely to improve much"]
From what I understand, Onkyo's have an incomplete soundstage. Also, Japanese receivers tend to be a tad harsh and lack warmth.
I forgot to mention, I also plan on buying a seperate Rotel amp... which should also help.
["Both Onkyo and Rotel make great, well-built solid state amps"]
...but they don't play in the same league. Why else would Onkyo bother with their Integra line?
Rotel can play with the big boys like Krell, from what I understand... granted, Krell beats Rotel, but apparently, not by much... and Rotel does it for a lot less money.