Dave
Onboard speakers are never going to give you a real evaluation of what the audience is hearing and was my reluctance to even using old style wedge monitors for years. I briefly used one of the ones with s 4' speaker on a mic stand but didn't like what I was missing. And personally IMHO I think they make a keyboard look less professional )
I keep one of my Eon Ones off to the side of me and with its dispersion I can hear everything perfectly. It has made singing so much easier with its clarity. Put your Bose behind you and off to the side and it should give you everything you need to hear.