Short of getting a specialty build using Jensens, I'd recommend just (switchable) output transformers. I can't recall the details, but I don't think Jon thought the typical input transformers he uses (some kind of micro-transformer) is the best with PA-driven concert recording. IIRC the issue is that they will saturate too easily or something and that the frequency response will suffer (poor low end).
I'm probably garbling that horribly, but you might want to discuss this with Jon. My only take-away was that if you wanted a transformer flavor in a littlebox to be used for concert recording, your best off with output transformers. Swicthable input transformers would be an option for when you wanted to record lower volume stuff at times and wanted the gain boost offered by the trafos, but wouldn't be the option for getting a transformer sound to concert recordings.