Positioning Vandersteens

This is a two-part question and since the parts are related I think one post is appropriate. First part is regarding a recent thread about speaker placement in dealer showrooms in which a couple of folks commented on the difficulties in properly placing Vandersteen speakers. This is interesting since I am in process of trying to get my 3A Signatures properly located in my somewhat small room. I’m having difficulties, primarily with a bass boom, and was hoping someone might be able to relay their experiences with siting Vandersteens. Comments on whether these speakers are appropriate for my room (see below) would also be appreciated. The second part of the question relates to the room itself, I recently measured the room with my Radio Shack SPL meter (using the Rives Audio test procedure and the Stereophile Test CD) and found, to my amazement, that the room was only flat from 400 Hz to 1000 Hz, the readings dropping off steadily such that at both 100 Hz and 10,000 Hz the readings were 20 dB down. This seems rather extreme to me, anyone else have similar findings? Specifics on the room, overall it is 17’ 3” by 14’ 8” with 7’ ceiling, however, it is reduced in size by a partial, full height wall through half the width making for a 13’ 4” by 14’ 8” space where the speakers are. To make matters worse there is some ductwork (boxed in and insulated) running along two walls. Because of the odd shape most or all of the acoustic software for siting speakers won’t work. Particulars of the system: Audio Research SP-9 MK II, Audio Research Classic 60, CAL Tercet MK IV, VPI HW-19 MK II, McIntosh MR-71, and PS Audio P-300. Some assistance in this process from those who’ve been there done that would be greatly appreciated!