I own the SR009, HD800, HD600 and HE-6 from that list. I still don't have the Alpha Prime with me but I did own the Alpha Dog (sold them to buy the Prime) but I did listen to the Prime for a little bit last week.
Even that the AP and AP have great soundstage presentation for a closed headphone they are still closed and IMO will never have the same openness as the HD800 or SR009. IMO there is nothing like the SR009 with a good tube amplifier but then you are talking about $10K or so investment. The HD800 is one of my favorites but only when used with a good OCC Copper wire otherwise I personally find them a little bright. I am using my HD800 with a Zeus cable and they also have the wires form the connectors to the drivers of the same wire used in the Zeus. With my McIntosh MHA100 they sound fantastic and probably the best I have heard them.
the AD sounded very good with the MHA100 too but the soundstage is not as big as with the HD800 but on the other hand the sound more dynamic probably because of the enclosure.
Of closed headphones I have owned the DX1000, D5000, D7000, Edition 9 and still own a modified version of the D2000 and also the W3000ANV. i have listened to the TH600 (Ipersonally did not care for them) but I have never listen to the TH900.
IMO and based on your description of sound preference if you want a pair of closed headphones with no exaggeration on any frequency and good soundstage I would go for the AD or AP.