I'll try to listen tonight at home on good phones if I have time, yet have a trade show starting tomorrow through the weekend I need to prepare for. Sounds good on the cheap bass-less ear-buds at work.
Not sure about summing all omni too mono at that relatively high frequency. I usually prefer the opposite (increased wideness in the bass) for spatial reasons, unless the bass or kick are oddly uncentered or lopsided for whatever reason, and consider that width one of the main benefits of spacing the omnis widely. There is a good argument for monoizing or at least using less width at the lowest octaves however, say under 80Hz, for maximizing low frequency reproduction energy from small woofers. At mid and high frequencies above 400hz, you are still getting the benefit of the omni spacing with regards to decorrelated reverb and ambience providing good "openness" in that range.
Have you tried a mix without the monoization? Or pushing that monoize cross-point down low? Worth comparison I think. Of course what is right for your recording is what sounds right to you!
If you like monoing the bass below 400Hz, try this alternate mix method to see if it helps with bass quality: Instead of summing both omnis to mono below 400Hz, try using only one or the other of them panned to center or duplicated to the other channel. That will eliminate phase interaction between the two which is occurring in the sum due to the spacing / wavelength relationship. The same phase interactions which provide some of the qualities I prefer in stereo bass reproduction (above the lowest octave or two), may be muddying up things when summed to mono.
And in general, I agree with Heathen about EQ being a goto for tweaking the midrange, and dynamic EQ helping the mud-range.