So I ran a similar rig with no preamp prior to getting my MP-2, and was pleased with the results. I did add a couple of AT transformers to give me more gain to work with, but the results were good. Lineage was
391(s)>B18s>AT CP8201>Mod SBM1>D100
A couple of examples of this combo are posted here...:
http://www.archive.org/audio/etree-details-db.php?id=5385http://www.archive.org/audio/etree-details-db.php?id=1693Also, I would probably stay away from the extension cables for a couple of reasons. First, they are expensive, if I could get a pair for under $200 I would probably do it, but $400 + is absurd. In addition, they are useless in my opinion for stealthing if you have to go through metal detectors. The cables do nothing more than move the bodies farther down in the chain so you still have to use (and find a place to smuggle through the detectors) the solid metal body. The only advantage I see of the cables is a lower profile stand, and if you do stealthing where wands do not come into play.
I don't think you would be disappointed with the 391's. In my opinion, at their price point (~$400 used) they stand alone. They blow the Oktava's and C1000s away, and probably the only earthworks mic I would use over them would be the SR77. The 480's are a different class of mic, but I don''t believe you will be disappointed with the 391's.
If you have any questions I could answer, just drop me a line.
Nick