9.1 speaker setup question

[mugupo]

I had Onyko 9100thx home theater system which is 7.1 speaker system, i check the receive it has 2 more slot for "B" speaker front, i notice there's a option for turn on speaker A & B. I wonder i add 2 speaker to B (Front) i can get 9.1 I notice THX and some other setting can convert 5.1 to 7.1 but it will do the same for 9.1? is it even worth to upgrade to 9.1.

I saw amazon selling sony b1000 bookshelf speaker (pair) for 49, consider buy it to add as 9.1 for (speaker b front)

http://www.amazon.com/Sony-SS-B1000-8-Inch-Bookshelf-Speakers/dp/B000OG88KY/ref=cm_cr_pr_product_top

Should I do it?