What are the sonic differences between…

I understand why you wanted to keep this general, but can you at least say whether the sub will be used in a HT, music only, or some mix thereof? Might help surface some useful information on one or both of the subs you're looking at, or maybe introduce some other potential options. Just a thought, and best of luck in your search.

Here is my equipment:

Pre-Pro: Anthem AVM 50V
Amplifier: Anthem PVA 7
Center: Paradigm CC570 v.3
Fronts: Paradigm Studio 40 v.2
Surrounds: Paradigm Studio ADP-590 v.1
Rears: Paradigm Studio 20 v.4
Subwoofer 1: Infinity Intermezzo 1.2s
Subwoofer 2: Paradigm PS-1000
Subwoofer 3 (new, unopened, not in use): Def. Tech. Supercube 4000
Source Blu-ray player: Oppo BDP 95
Projector: Panasonic PT-AE4000U
Power management: PS Audio Power Plant Premiere AC Regenerator

I have a vaulted living/dining room that is 24’ long and 15’ wide. The screen is at the front (8’ end) of the room and the listening position is about 12’ away, with the remaining 12’ behind the seated area. The vault is 16’ high, at the back of the room, behind the seating area. The floors are hardwood and the walls are sheetrock. We have two sofas, two bookcases, a table, a buffet and some things on the walls. The main use of the HT system is for movies. The sound, especially the dialogue, is not as clear as I would like (i.e., not as clear as the theater I built in the basement of my old house). I have an opportunity to get a subwoofer at a great price: A used, 2007 Velodyne DD 18 (with room correction) for $1,700, or a new Paradigm Sub 1 for about $2,200. In reality, most of the problems with the sound are due to the acoustics of the room, but who can pass up a deal like this for one (or both) of these subwoofers?

More... The front, right half of the room opens on one side with a ½-high wall to a closed hallway, and the back, right half of the room opens to another hallway and also to a second open area to a den. Basically, the back half of the room - with the vault - is open.

The CC is directly in front of the seating position and is tilted up about 30 degrees to aim directly at the listeners’ ear. The CC, fronts and Infinity sub are on a similar line facing the seating area, with nothing in between them and us. There is a large rug on the floor between all the speakers (including the CC) and the seating area.

The suggestion of buying one Sub 1 now and getting a second one later is a good idea. I like having two subs and having them matched will probably improve what I am hearing/feeling.

The last issue, that I didn’t want to muddy the waters with, is that we will probably be moving in 6 to 12 months. Unfortunately, we don’t know where we are going. But at least, we will be taking our HT equipment with us (again :)