kirkd, I support what DATBRAD is saying about transformers, particularly for long cable runs. The ability of a balanced preamp input to block out interference depends on the balance of the
entire circuit, microphone+cable+input. Microphone cables, unfortunately, are never perfectly balanced, and the longer they are, the greater the risk of significant imbalance. Active balanced inputs generally don't reject interference very well under those conditions.
In recent years a circuit technique has emerged (see
http://www.thatcorp.com/datashts/dn133.pdf if you're of a mind to) which could help a lot with that, but not many manufacturers have adopted it yet. Maybe if people like us were to be better informed and more demanding, that situation would change. Also, many MANY consumer and semi-pro recorders and preamps still have "pin 1" problems (go ahead, look at
http://pin1problem.com/ -- I dare you!) which create paths for interference to be amplified rather than rejected. It's amazing how long it's taking for certain manufacturers to become savvy on these issues.
The whole thing about transformers sounding "warm," or in fact sounding any particular which way, is something of a myth, or at the very least a "myth-underthanding." Transformers in old microphones such as the original Neumann U 47 are a whole other topic--they were part of a design which was carefully tuned as a whole, and the net result depends in part on certain technical shortcomings of those transformers, in today's terms. More recent microphones that were designed to be transformerless are surely better off without them. But the input transformers in the Sound Design class of preamp aren't a "sonic factor"--they're a practical approach to a necessary solution.
--best regards
P.S.: Someone earlier in the thread was concerned about 15-Volt phantom powering and Schoeps microphones that are designed for 12-Volt phantom powering. That voltage difference isn't a problem as long as the other parameters of the power supply are correct.