Phil,
We have had no problems with the unit at all. Our Family Room is pretty big, and when my wife gets a crowd of those Chinese women together, they rock the house

. As to stereo speakers, we use Thiel CS-3.5 speakers in the Family Room (where the Karaoke stuff is done). Our couch is ~ 12 feet away from the speakers, and we have never had any audible feedback in our home (even at high volume).
Actually, she has also used it in several auditoriums (for the Taiwanese Association of Tampa Bay meetings). Keep in mind, the two microphone inputs have their individual gain controls, so you can determine how loud the "vocals" are relative to the rest of the music. And she uses this machine as her PA system for their "guest speakers". It works like a champ.
But the speakers she uses for here group meetings are VERY entry-level type stuff (to include VERY entry-level amp/cables). In this scenario, I have once heard feedback, but ONLY when the person speaking stood directly in front of the system (2 - 3 feet away) at high volume. All they had to do was move a couple feet away, and the feedback disappeared.
I can say that in almost every situation, feedback has been a non-issue. And when it did rear its head, it was easily defeated. Simply keep the vocalist/orator from snuggling up next to the gear/speakers, and feedback will not occur.
Kevin