Sounds like you have a lot of load and stray capacitance on that combined track system. If you have more engines on the track, lighted cars, anything that draws power, you tend to load down the DCS signal.
Also- other factors at play:
2rail/3rail trucks on engines- may or may not be getting good clean power and signal- could be at the trucks or could be at the 2r/3r switch.
PS2 I find generally has a lesser signal reception than a given PS3 engine, however, wire routing in the engine past the boards is one known change that can affect any engine and it's DCS interference.
Things you could do:
Inspect engines, toggle 2rail/3rail power switches on engines that have them, inspect the wheels and trucks, use lighter conductive oil on those bushings and contact points.
Split your track plan into blocks such that the main loop is one DCS channel, and then yards and other details are another DCS channel- possibly using your variable channels.
Another thing, and this just bit me over the last few days while testing a DCS explorer- for the first time ever, I had Legacy signal interfere with DCS. I normally get 10s all the way around using my revision L TIU. However, for testing a few scenarios, I unplugged my TIU and swapped in a DCS explorer. It was immediately obvious I could not add or detect any engines. Turning off the Legacy base, suddenly the explorer worked just fine on my track. So again, with a mixed result like that- my TIU works fine and there is no problem, and then the DCS explorer on the same track system with Legacy and there is interference.
At the same time, I have a scenario at the local club where the table is 75 feet long, making the outer loop 150+16 feet of track, and inner loops not a whole lot shorter, and yet we run a TMCC/Legacy booster and DCS and still get 10s on all 4 tracks. And, we have the booster turned up (I do have the variable control added) . Also, I'm running that TIU and all 4 channels fully passive with 22uH chokes in series with the Z4000 transformers for each track. So in theory- I'm in an not ideal scenario- and yet we do not have massive interference.
RF and signals is and can be tricky, so I know that does not help when you are having an issue and trying to figure out solutions.
