For the connections between boards I used all shielded cabling. The shield is connected on one board per connection as I have all of the 0V connections connected to the star ground as well as the chassis solder pad that connects to the ground plane. This seems to prevent any ground loop between the boards and blocks radio/EMI interference, which is something I have to consider where I am.
External PSU or switched internal is recommended for this design. I have built other units that used a different Neve style preamp card with the toriodal transformer on the opposite end and experienced no issues, but this does not seem to be the case here, even with Mu-Metal shielding that I'm using for my build. JLM audio has some very clever SMPS units and PSU boards that address this issue. I have some on order that I will swap with the PSU I currently have installed when it arrives. I did find that when I attenuate the output about 10dB this makes the noise inaudible, and there is still a ton of gain. I have found that I really can't go any higher than 40dB talking into a dynamic microphone before I've reached the headroom limit on my converters, so there's plenty of room to work with if I decide to rewire the output transformer for lower level. Still, I will swap this with the JLM solution when it arrives. and use this for future similar builds.
Something else that I guess I should have mentioned first is to use the provided schematics for these boards as a guide for component designations and not the BOM as there are a number of discrepancies. Some of the changes were based on alterations to suit different tastes while interacting with digital audio, but I found just using the original values yields a great sounding unit.
These are really handy boards for standalone operation as well for make up gain in summing amps or building a stereo EQ rack. and I found it's one of the easier ways to build an authentic (based on the original unit's serial number being used for comparison) 1073 without the need for all the original cards and intricate wiring network.
Thanks!
Paul