OK, I just tested the T58 with a D12 retrofitted with a '90s AKG D12 capsule on a bass drum. There were some interesting results, to say the least.
First, I ran it into the Vac Rac pre. I had wired the transformer in the same in/out direction as the SM57. (At least I think I did.) What I initially got was a serious reduction in the lower mids, with pretty much the same over all gain. I changed the direction of the transformer, and the improvement was huge, but I lost -12dB of RMS gain. I got all those mid lows back, plus the low end was more defined. More important, there was a better transient attack, and the transient had more full range to it, where as without the T58, the transient was missing the lows and mids.
I then ran it into my usual 1073 that I use for kick, with my usual EQ: 12kHz shelf at 9:00, 360Hz at 3:00, and 110Hz at 8:00. This time, the T58 only was losing -3dB, but the sound improvement was huge over the non-transformer recording, to my ears. With the highs boosted, you could hear what that difference in the transient was with the Vac Rac. Without the transformer, there is a boosted high frequency, but I don't know if it's something I like, at least on bass drum. The T58 seemed to attenuate the frequency response in the 15kHz range, and put the power back into the low end, where it belongs. This is for sure my new Ludwig bass drum configuration, from now on.
My high end attenuation theory was confirmed when I tried the transformer with a Heil Pr30, which is a very, very bright mic. I don't know if this is a qualitative situation, with the high end response. It just might make it better suited for some capsules, the way that the T14/1 was better suited to the low end of the CK12, than the original T14 was. But for my ears, the T58 is better suited to the D12, and particularly more so than the original transformer, which I quickly recognized as disliking more so than bypassing it.