I would say get a demo to know for sure. Have you got access to both 009 and Utopia? I thought you already had an opinion on the 2 together? I would say get more time with both before you push the money trigger. It is a big spend and only hearing these two will resolve it IMO. Peoples preferences and amp / DAC choices come into it a lot, even how loud they play them as well.
I haven't heard the Utopia yet, but I would offer my opinion on the bass quality of the 009s. I have big horn speaker in my HT system with 12 inch bass units and augmented with a Velodyne sub. So my HT system goes down to below 30Hz and is fast and dynamic, partly as my room is not so big and I am sitting really close.
The bass on the 009 is faster and more textured than my speakers, possibly not as forceful but you get room pressurisation in a speaker system, something very difficult to replicate with headphones. Bass quality is spot on with the 009s IMO, if it was increased in level it would, I am convinced smear the mid range and treble and muddy the soundstage and reduce the 3D image. Remember the ears get fatigue with too much bass and will react by 'closing the shutter' so to speak, i.e. reducing the reception coming into the ear.
I listen to lots of genres and bass demanding music such as trance and house music sound great to me on the 009s. Lots of drive and pace, really damb good. I really don't feel any need to up the bass at all. I have done that in the past with digi EQ by around +2-3 db before I finished my DAC tube rolling. But now I feel no need of it. Tyll in his review upped the bass EQ on his Utopia by 5dB I believe.
My other thoughts / theory on the bass output is, unlike a 'normal' house speaker system with 2 or 3 way designs, the 009 and most other HPs are single driver. If that driver has to produce as ruler flat and fast response as possible to provide the illusion of a live music event, it will have a hard time indeed getting loaded up with too much bass energy.
Also 'maybe' folk coming across from V shaped HP's (massive generalisation and not meant as an insult) they may well find the Stax model too different?
I guess no HP will be perfect, relate the live event with the huge dynamic power and 3D image that can be experienced. But the 009 IMO gets me close enough, close enough to forget the gear and track swopping and sit back and chill with it. Sometimes late at night, and putting the 009s on they blow me away to another place, they are that good IMO.
I do also believe they are ruthless at revealing upstream gear, a microscope to what is going on, so much so it demands more investment elsewhere or the owner will never be happy and have to move on....
Hope this helps