If the stands will be a problem or you don't like the WAF of the stands by all means wall mount some bookshelfs or on-wall. The most critical of the surround speakers are the side surrounds in a 7.1/9.1 setup. A pair of QS8 will give you the best performance in theory as surround backs but the surround back speakers are the least crucial of all the speakers in a home theater setup. Very little content goes through there and it is not very critical and demanding content either.
You could definitely use the 3.1's in a 9.1 setup if you like.
