Earlier in my boating career, I got to boat in South and Central America quite a bit.
Ecuador is to me the gem country for boaters. I ended up making some 5 trips down there.
Phil and Mary DeReimer is the outfitter I used (they do small group, personal attention to individual skill set just awesome couple), with Small World Adventures (one of the first outfitters there and what a River Lodge they have) and Endless Rivers (Ken Kastorff. another first class river front lodge) all these folks offering first class boating experiences.
We always flew to Quito then drove to Baeza over the mountains and from Baeza over to Tena for awesome rivers based out of both cities. Been a few years but I bet they still do similar areas.
I recommend you do some research on the above outfitters and ask about possible day trips with them. There are riverside lodges there in the Baeza area that will just blow your mind with the food and facilities. Gina's there in the Baeza area is the place to hit for good food. You cannot miss with her Trout dishes.
If possible, get there a few days early and sight see in and around Quito. So much historical sites to see and just experience that city.
PS: I never saw piranhas, snakes and no biting insects anywhere, maybe I was lucky. Also do not miss the hot spring setup when you travel over the pass getting back to Quito.