yes, or whatever

>>Pass amps

yes, but there are more affordable choices that won't affect
performance.

>>or possibly wire all the drivers up in series and build OTL tube
>>amps for the mids and tweets.

I don't consider this 'ultimate', I see it as counterproductive.

>>Jordan JXr 6HD

Yes, but there are better line array designs that using 2" drivers.

>>I think the dipole guys are onto something

Personal preference design. Coke or Pepsi ?

>>Tweets - I don't think this is quite as important as the rest

The tweeters will be the heart and soul of your sound system,
this is where you need to focus on.

>>TC Sounds 12" aluminum woofers [40hz to 300hz]
That would be pretty good, not ultimate though. If you want
ideas, email me.

>>Aurasound 18s

yes.

This is the easier part, building a monster subwoofer. Many
woofer candidates that can do this job well.

>> I will listen with these speakers roughly 9-10 feet apart and
>>9-12 feet from the listening chair

I would make a tall array, not shorcuts in spite of a short listening distance.

>>So I think I only need four Fountek NeoCD 2.0 ribbons in each
>>speaker, again running 6kHz on up.

Regardless of the design you choose, four tweeters is a compromise,
do a full blown array with mids and tweeters.

>>Still waiting for someone to convince me that the Jordan JXr 6HD
>>is not the ultimate starting point

Building any loudspeaker begins with quality tweeters. Great midranges mated to 'ok' tweeters never sound good. On the other
hand, quality tweeters with 'ok' midranges can be made to sound
much better. You need to focus on the tweeters and then the midrange
quest is so easy. I can tell you right now that finding exceptional
tweeters is a more difficult task as the market has very few to
choose from if you want to make a line array but the market is
saturated with quality midranges or midwoofers that can easily do
the task.

Stay away from this type of design, you can do better DIY style.
http://www.mcintoshlabs.com/mcprod/shopdisplayproducts.asp?id=20&cat=Loudspeaker+Systems&prodid=1114&product=XRT2K

>>I would go active between the woofer and mids, and passive between
>>mids and tweets.

Go 100% active, don't waste your time with passive crossovers.

>>go Pass DIY for the amps

Those DIY amps are low powered, low headroom. An array deserves
more power and headroom if you want to exploit it's potential,
otherwise you will be just an average Joe with a good system,
but not ultimate system.