Would the 990/7125 be a significant upgrade compare to a Pioneer elite vsx 49 txi, I like the sound quality of the elite but i would like something that can drive a 4 ohm set up, any comments?

External amplification will always be an improvement over a receiver's amps. I am currently in the process of comparing the 990 to my Pioneer 54TX (used as a pre only). They both have pros and cons.