Last year, I bought a pair of Polk Monitor 40 speakers and a Onkyo 8050 Rec. I really like my set-up but I may try to improve on it. I am thinking about adding a subwoofer, but I have some restrictions. This set-up is in my bedroom. I do not want a large sub nor do I want to run a sub cable around my bedroom or up into my attic. Iam thinking about placing a small sub on my bottom shelf of my componet rack. the sub would have to be less than 12 inches in height , 18 inches across and the shelf is glass. My speakes are only 25-30 inches apart so the sub would be between them. Is there a problem with this set-up? I heard it may not be a good idea to place a sub on a shelf or close to your speakers. I was looking at a Yamaha YST-FSW50 or YST-FSW150. I would like any suggestions.