There are a few great subs out there and I had done alot of research on them in the past month or so.Paradigm I heard and they are nice,but in the value department considering price I came up with the with the NHT Subone(i).For $400US bucks(list $800) it was hard to overlook.I have a few set's of speakers which I switchout when doing serious listening and the Subone gives alot of versatility for playing Music and movies.
The music playback is great since adding the sub and the more I listen ,the more the Bass is openning up.I have a pair of Magnepan 1.4's and anyone that has Maggie speakers and try adding a Sub find it can be a real pain.The Controller allows to customise more easily. adding a Lexicon CP-3 Pre-Amp processor which will be the main controller in the system will also give me more flexibility.

Velodyne--Servo-controlled models
M&K
B&W
Pardigm

All make great subs also,but the price was an issue for me when selecting a model.Plus how flexible the unit is.I could have bought the Paradigm PDR-12 I believe the model was,but it was smaller 10" vs. 12" and did not have the flexibility which I sought after!

The Axiom which is rated at 35hz. is probably a fine sub and I think trying to get the magical 20hz or less plateau is not criticle.Most people can not hear that low and most all music does not go to these depths.If you love that Organ pedal and need it that you want to pay $600US+ for then I guess you will have to fork it over to the man!But as for myself,If I can be happy listening to the Octaves of bass rolling up and down.If they blend well with the overall system sound without getting in the way at the crossover meshing point then I am as happy as a clam!

Subs Heard and Owned
Paradigm Pdr-12(Wanted Flexibility)
Velodyne's--Got one for a friend nice unit!Sound is great!
Jamo's--(I liked it,but it got damaged in a storm)Similar specs to the Axiom EP-125.
M&K---THX designation means zero to me!
B&W--To pricey
HSU Research--Does not dissapear from the room!Hate that!
Subone(i)--Can't beat it for the price and it competes with the Pardigm.Pw-2200 at half the price!I can live without the 5Hz. loss at -3db.Rated to go to 20Hz as opposed to 25Hz. with the Subonei.