John Groover McDuffie wrote:...the benefit of the Uni that I am interested in is the lack of a string between the 8th E and the B below.
Fortunately, I had never made much use of the D string on E9, so having it on a lever for occasional use didn't bother me when I switched to uni. On 10-string E9 my thumb had learned to always skip the next-to-last string (except on those rare occasions I wanted a D), but on Ext. E9 (which I tried before trying a uni), that D became "some string down there in the middle of a bunch of others," and my thumb just couldn't take the confusion. When I tried a uni, that whole problem dissappeared, and I just felt much freer on the low strings. And when you play in B6 mode, that D is a useless string mucking up the heart of the 6th tuning.
A lot of this choice depends on what type of music you intend to play. If it will mostly be country, and you make a lot of use of the D string, then Ext. E9 may be your best bet. For country E9 I don't make much use of the low strings of a uni, and I could just as well stay with 10-string E9. But if you want to make extensive use of the 6th mode (and you don't want a D10), you really need a uni. I look at it as trading the single D string for the whole 6th neck tuning. Once I tried the B6 mode, that trade was a no brainer for me.
At this point I'm not too worried about the low low B.
Ah, but you don't know what your are missing. If you raise that 12th string B to C# on your A pedal (just like the Bs on strings 9 and 5), that provides the low root for the A pedal minor position. That gives you the low power chord (strings 12, 10, 9) for minor blues and jazz, and over two octaves of minor pentatonic notes (releasing the A pedal gives you the b7 on strings 9 and 5). Since I love blues-based jazz, that has become a more important jazz home base for me than the 6th neck mode. Move down a fret and add the B pedal and you have V. On LKV I raise string 7 a half-step, which makes that a V7. From the A pedal minor tonic position, if you release the A pedal and go up two frets you have IV, two more frets up is another V. If you keep the A pedal down at those IV and V frets, it makes those M7s. So the A pedal gives you a movable M7, so useful in jazz. From the A pedal minor tonic position, if you add the F lever and move down two frets, you have the bVII, and three frets down from that is the V. So holding the A pedal down and griping strings 12, 10, 9, you can march up and down the neck on the pentatonic frets for a power chord pentatonic scale - dynamite for blues, rock and jazz. I couldn't live without that low B string.
On Ext. E9, some people lower the low E to C# on the A pedal, but it doesn't have the same tension, punch and sustain as raising the uni low B string to C#.
By the end of the gig I was totally used to the missing D and getting it on a lever. I know you want that open D there, but why not if you get a chance try a universal somewhere...you "may" like it, you may not....at least you'd get another insite by actually trying one for a few hours. If it's still a no no for you on the D note, it's back to your thinking cap. Wishing you and Suzie in advance a happy and above all healthy Christmas. Keep the equiptment light 
we're both pushing on now 
)
