Haven't tried the Karma mics, but we bought the T3 and have been very happy with it. The multiple patterns and the "airy" quality of the T3 has proved very useful on a lot of singers and various instruments.
...the guy here who has the most experience with these mics is probably ljmaxx, but I can shed some light on the T3 and K6...
...both of those mics have endured the "survival of the fittest" evolution of my personal mic closet...the T3 has seen many of my other Chinese tube mics go up on the auction block because they just don't offer the same balanced sound (none of the typical shrill high-end or lacking mids) and multi-pattern versatility...IMHO it stands as Studio Projects' best mic to date...best "bang-for-the-buck" multi pattern tube mic on the market...excels on both male and female vocals, as well as cab and overhead miking...(other tube mics that remain as "survivors" in my closet are the MXL V77, Rode K2, Cascade/sE V55 and Mojave M200)...
...the K6 also has outlived a few of my other Chinese ribbon mics as well...the "phantom-powered" feature makes it more versatile in terms of pairing it with asst. mic pres due to it not needing the typical 60+ dB of gain to get it started...it's very smooth and somewhat reminiscent of the classic ribbon mics of the past...again, another "best-bang-for-the-buck" winner, especially if you can catch Karma's frequent reduced-price offerings...it's outlived my collection of various Nady, Apex and Stellar ribbon mics...the only other ribbon that offers great value that I'm aware of is Cascade's "Fat Head" which seems to garner much positive approval on the audio BB sites...
I have a K-58 and two K-6's. The K-58 made my Rode NTK expendable (particularly once I swapped out the 12ax7 for a NOS GE 6072a tube on the advice of kidvybes and ljmaxx) as I found it to be a much smoother and less sibilant microphone (plus it is a multipattern microphone). I have no experiences with other ribbons, but I've used the K-6's on vocals and acoustic guitar (just got a little tube amp and attenuator and will try it out on electrics next) and found that it sounds great. As kidvybes mentioned, the phantom power gives the K-6's a robust output (relative to what I've heard other ribbons produce), plus you don't have to worry about accidentally destroying the ribbon with phantom power.
The Karma folks are also really nice and very committed to customer service. It's nice to be able to call them up and chat with them about their products.
All 3 of the mics you are asking about will give you very good results. I have all 3 of them and they all get used depending on the vocalist. The T3 has a little more top end sheen to it but on some vox that's a good thing.
The K58 is IMHO the best of the three mics you are asking about as far as a vocal mic. It seems to let the vocal sit in the mix without a lot of tweaking. It is also my favorite vocal mic on most male vox after I swapped the tube out with a GE 5 Star 6072a .
The K6 offers a different approach to vocals since it is a ribbon and as kidvybes pointed out it is phantom powered which makes it easier to match up to mic pres with less gain required. This mic works well with a lot of female vox.
Thanks for the spot-on replies. I think I'm going to grab the K58 while it's on sale, and probably just buy the K6. I'll keep the T3 on the G.A.S. list. Thanks again.
