ML Dynamo 1000 (discount) or custom box Rhythmik, help

I have a chance to get a Martin Logan Dynamo 1000 for below 50% retail. My previous plan was to order a Rhythmik 12" or 15" and build a piano gloss sealed box with my friend who is a carpenter. This would save me a few hundred from the F12SE, and get me a what I am told is a fantastic sub (I believe you guys on this one). I'd prefer sealed, and piano gloss as I have BW CM9s in piano black.

I can a) buy the ML Dynamo 1000 and either sell it later for a Rhythmik or.... buy a second Dynamo for two 12" subs

b) or I could never bother with the Dynamo, and go straight to my original plan and get Rhytmik (maybe a 15"), and a second when I can afford it.

c) get the dynamo and mixmatch with the Rhytmik.

I have a Marantz SR6006, and I use my setup for video gaming, movies, and music (about equal). I tried to spec things to a musical side, and would like to continue that. I am in college for another two years, so budget is important. My current sub is a JBL 100W 10" woofer.... PS100 or something like that. Obviously anything above is a huge upgrade, but I am willing to be patient if worth it.

ANY input welcomed, as long as it is constructive.

bumping once only.

The room is as shown at the bottom in an img file, however is roughly 19' x 11' - 14' depending how you look at it.

The 15" Rhythmik is a great price over 12" if going custom, but the size is so huge. I currently am living with my folks so a 15" is no issue, but whatever place I can afford when I graduate may fall down with a 15" sub in it ha ha. I am also semi-concerned about future WAF (how sad). You guys who own 15"s do you have them in a dedicated theater room or right in the living room?

Are two 12s (Rhythmik) better than one 15?

To answer Jim, I get a deal through my job. I am impressed by the Dynamo 700, but from what I read here its probably garbage compared to ID. I have no reason not to believe that advice, so I am OK with waiting rather than jumping on a ML just over the low price.