trying to learn how to wire xlr in and out to 4 transformers

Hi Justin -

It seems like you are missing a few puzzle pieces here. Transformers are described as a turns ratio, not impedance measurements. A transformer has no inherent impedance (an input xfmr will have a non-negligible DC resistance but that's something else). Rather, it will literally "transform" the impedance of the input load as seen by downstream devices, by turns ratio squared. So the impedance measured at the output of a transformer depends on what is connected to the input terminals.
Connecting a load to the 600Z pair of terminals on each side is simply a 1:1 isolation transformer which will give galvanic isolation, and change neither the voltage nor the impedance of the signal source as seen by the load. 1000:600 is a voltage step down of two thirds (.6V out for 1V in) and a Z ratio of two thirds squared, or 0.3, so a standard 200Z mic would look like 60 ohm to the line.
Modern audio devices should be interconnected using impedance bridging, not impedance matching. The 600 ohm dog is dead. It is a holdover from telephone and tube interconnect and will cause large signal loss with modern devices.
So I guess I am not clear on what your desired outcome is with this project.
In any case I would advise using plastic XLR housings to isolate them from the chassis.

I'm really just trying to understand exactly what you are trying to achieve by connecting 4 transformers in series to your mix buss. Are you connecting some external input device to your mix buss? Are you combining your mix buss to output an external device? If so, there are other ways to do these things. In the meantime, you're melting my brain (which is already pretty soft, Ha Ha)

Thanks, Rock, you make some points that I needed to know. What I want to do is simply add these transformers in a 2 channel config, with 2 in series on each side. I want to put them after my DAW, my interface, and an SSL Fusion (the latter which I read has an output impedance of less than 200 ohm). In reading about transformers being used like this, some people have written that they can be dangerous to modern IC based gear, because they can overload the amp. One person said that sometime low frequencies in the transformers can lead to a "dead short" which could be extremely bad for IC based kit. I don't know if any of that is true, and it did seem as if people are using a variety of transformers in this application, including some output transformers.

I have read that as long as the input impedance of the transformers is more than the output of the SSL FUSION then I'll be okay, but I don't know if that's true.

The transformers I have purchased were supposedly used in a DI for a radio station. That's all I know about them. Googling that company Transonic, turns up very little, and it appears they went out of business in the early 1960's.

I think your alligator clip idea makes the most sense to start testing. My remaining problems are: I am not sure how to wire these in series and keep them 1:1 ratio, and, I am not sure of any risk to my IC equipment, like a "dead short" etc.

Thanks, Rock. I will try to track down that article. Just reading the comments that come up on your link, it seems that I probably could stick with the build I am already hoping for, since I have transformers that are very old, and will probably sound like transformers. I am still not sure how to wire the ones I have, but it's true that more knowledge is a good, even when it doesn't answer my questions.

Many thanks. I will read up first before attempting to follow your suggestions. Thanks again

Again my suggestion is to wire ONE (1) and get it to work. If that works OK then just wire the second one in just like the first. If that works and you really want two in series, we can talk about polarity before you make your final build. If you study enough, may be you can answer the polarity question for yourself! I'm not going into it now because it's detail we don't need right now. Just get one working first.