Hey Brad,
Correct me if I'm wrong, but the only difference between a "Warm mod" and a "Concert mod" is the warmth? Therefore, a "Warm mod" is a "Concert mod" also.
Yes, both the concert and warm mods optimize recorders for the kind of high sound pressure recording concert tapers primary do. The headroom provided by the stock analog inputs is too low for taping very loud sources, but they are just fine for the type of recording the target customers, dslr users, would encounter 99% of the time.
In the Concert Mod, the opamps are upgraded and are still using bipolar transistors, but are better chips with lower noise and higher overload points. The Warm Mod produces the same headroom extension, but use FETs which are warmer in tone. The preamps in recorders and mixing desks during the 1980's and earlier used transformers and the first transistors considered viable replacements for tubes were FETs. Because of this, many tapers using older microphone models from that period find that FET driven preamps are a better match with these older designs.
The Concert Mod uses bipolar transistors with more headroom and lower noise, but are transparent like the stock chips, which makes them a better match with certain mics than the Warm Mod.
Doug also does a FET and Super Mod for ambient sound recording that does not increase the headroom as much, but are even lower in noise and THD.