OK, have a look at this.
Ya, why?
And of course this connection is optimal.
The Emotiva UPA-7 is a 7-channel power amplifier. Are your speakers bi-ampable? Is the Emotiva able you to bi-amp your speakers (ya)?
If yes, you can use two amplifier channels to power one of your main front Left speaker, and two more amplifier channels to power your main front Right speaker.
Is your center channel bi-ampable? If not, you still have three power amplifier channels to power your center speaker and your two side surround speakers.
So, your RX-V3800 will only power your rear surround speakers.
And why did you get an Emotiva UPA-7 in the first place? Don't tell me; to make certain that you have enough power for all your speakers and that you can crank the volume level higher, and also because the UPA-7 is such a great deal and looks simply gorgeous!
Are all your seven speakers are bi-ampable. If so, you can use the seven power amps of the Emotiva UPA-7 to power the low frequencies of all your seven speakers, and use your Yamaha RX-V3800 seven power amps to power your high frequencies of all your seven speakers!
And why would you use only three power amps from the UPA-7, while there are still four more just idling and doing absolutely nothing???
Do you have some more questions to ask?
Bob