So I actually figured this out, As long as the Legacy system isnt connected to any block that has a wire straight from the TIU the DCS engines work perfectly, even when the VL Big Boy is sitting right infront of them.
So I have been having strange connection issues with my DCS engines on my layout. Some areas on the track signal test would get 10s, some areas would get 4-1, and most the DCS remote would scream check track and Out of RF range when i even try to start the signal test. It turns out the areas with 10s didnt have any TMCC or Legacy engines on the track block, areas with 4-1 would have TMCC diesels and areas that would scream check track and out of RF range had TMCC/Legacy steam engines and Legacy Diesels. To test all this I used 6 different engines. For the DCS signal test I used a PS2 Rs-3 and a PS3 Veranda Turbine. For tmcc diesel i used an older TMCC SD60 from about 2004, for TMCC steam I used a tiny K-Line Pennsy A5 Switcher, For legacy Diesel I used an NS Heritage ES44AC, and for legacy steam I used a Vision Line Big Boy. So something as small as a K-line A5 had the same kind of DCS signal disruption as a Vision Line Big Boy, Both the PS3 and PS2 engine suffered the same horrible signal when any kind of Lionel engine was on the track. Keep in mind these Lionel engines arent running or doing anything. They are simply sitting there getting the Legacy systems command of not going into conventional mode. As of right now I have not even a full loop of track but it spans about 35 feet straight and then has 1 full 072 curve at the end. I use atlas track and drop an atlas power feed every 8 ft and then put an insulator pin on the center rail. The black coating of the center rail has been worn down on all my track. My TIU is a rev L and is powered by a Powerhouse 180. I have done testing on all 4 different ports of the TIU and same thing every time. I connect my Legacy with a wire to the common of the TIU. If I take a Lionel engine off the track the DCS engine instantly gets 9s and 10s on the test from getting 4-1 on it when the Lionel Engine was sitting next to it once again not even running. The track and engine wheels are clean.
I am Honestly baffled by this problem and Have no idea how to fix this, I am worried my tiu could be busted and have signal problems, its like the Legacy systems simple command of keeping in engine out of conventinal mode is louder than then entirety of my TIUs commands to DCS engines. I know its extreme common to run DCS and Legacy together thats why I find this problem so baffling. My Lionel engines run fine regardless of what kind of engines are on the track.
This is a very large post but I am honestly entirely confused and do not know what to do.