whoom instead of BOOM


hi everyone. new into home theater(though been running loudspeakers off a tv since the early 80's). anyway, i'm having a problem with the low frequencies. at the volume at which i get the spls i want(pants rattle a bit, couch vibrates etc.) i get a whooom response and not BOOM and lose definition and clarity. is it possible to acheive these spls without the "whoom" mucking it all up?
the room: 35x25x10 it is not closed in completely
the system: mirage m5si fronts, mirage 595si rears, mirage om-c2 center, mirage bps 150i sub(also working with dialing in a polk psw12 sub together), onyo txds797 processor. the front end is a panasonic dvd-s97.
THANKS!!
uncertainsmile
everyone thank you for your input. i think i may have led us all down the wrong path. 10x18x7 are the exact dimensions of the room, so it is not very big at all. even though a $5000 velodyne dd18 may be a solution it isn't quite my cup of tea. i'd go to a vmps or bag end type. however, i was more wondering if you all knew wether or not, despite decent quality subwoofers, is there a point where they may just get boomy and undefined sounding or is it my room, or are they really not that good. the mirage does sound fantastic at lower volumes. the best i've heard in my limited experience. i am lrking everywhere i know of to try and catch a vmps used for sale. it is tough unting ou there for one on the cheap. i may also go with a clark synthesis. thanks again guys.
Ahhhh I get it...

Clouseau: Do you have a WHOOM?
Inn Keeper: I do not know what a WHOOM iz!
Clouseau: Zimma
Inn Keeper: Ahhh.. a RRRUUUMMM!
Clouseau: That is what I have been saying you idiot! WHOOM!

You mean your Zimma is small and you want more vavoom for your whoom!
HA! very clever mr. bond.
james bond: do you expect me to talk?
evil enemy: no meester bond, i expect you to die...
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