Crossing to a sub?

[smbrown]

Looking for some advice... I am using an open baffle top end with a Fostex FF85K, which works extremely well if you don't ask it to go much below 200hz. At this time I have a sealed 12" woffer (an old Altec from a 70's bookshelf speaker) to handle the bottom end. So the setup is kind of Basszilla-like. My question is, is there any reason I could not use a subwoofer, like the Shiva, on the bottom instead? I'd use a sealed application since this is for hi-fi use and I don't want it overly boomy. From the graphs on the Shiva is seems to work fine up to 800hz or so, and I'd need to cross it in just below the 200hz level. Second question is, any reason why it would not work well in a down firing position if crossed this high? Third, the living room, where this will be, is upstairs and would downfiring cause a lot of energy transfer to the celing of the room below, or would it be really any different than front firing?
Thanks for any insights!

[BillFitzmaurice]

Yes, you can use it. No, downfiring is not a good idea for use above 100 Hz as downfiring will roll off the midbass. And no, placement doesn't matter vis a vis the transmission of vibrations to other rooms as the entire air volume of the room will be pressurized and will transmit vibration pretty equally to all boundary surfaces.