I'm going to say that the Emotiva UPA series probably won't make a bit of difference since that Yamaha is probably good for 70 watts per channel x 5. It just won't give you the headroom you will need for those volume peaks. I essentially did them same thing but on a larger scale going from 141 watts x 7 to 200 watts x 5 plus 2 running off of AVR -- made no difference in sound quality or volume. I was also going from a 7 channel to 11 channel setup and still needed an external amp. I ended up stepping up to a 400 watts x 5 amp which gave me what I needed for a really strong 5.x setup with the AVR powering the rest of the system. I think the XPA-5 at 200 watts x 5 is probably what you should go with provided your speakers can handle the power. Put your best 5 speakers on the XPA-5 and let the Yamaha power the rest.
I can vouch for a nice, powerful amp when listening to classical, especially multi-channel classical music. I have some nice 5 and 7 channel recordings of Beethoven, Mozart, Holst, etc., etc. that really opened up when I added more power.
Denon AVR X7200WA, Emotiva XPR-5, Emotiva XPA-7, Sony XBR 75" 850C, Oppo BDP-103D, Roku 4.
DefTech BP7000SC (L/R), CLR3000 (C), SM55 (FH), UIW BPZ/A (SB), UIW 75 (TM).
JBL L7 (Sur), EoSone RSR 350 (RH).
PC 2.1 setup. Emotiva Stealth 6, SVS SB2000 sub, Emotiva DC-1 DAC.