Below is a link to every MTH subway. You can identify the #6 route numbers in the appropriate column. Copy the model number for the 4 car train set that has a # 6 route, then go to the MTH website and paste the model number in the product locator search function. Then click on the subway set that come up. You will then be able to see a better picture of the model (you will see the window boards that may indicate your line), you can also sample the sound files for the engine to see if it has your station stops (click on the mp3 icon in the support tab), and review other information for that particular model. Hope this helps. I have one or two MTH models with a #6 route, but won’t be able to get to my train room to check for a while. However, this should get you what you need.
http://www.tcaetrain.org/2d-ar.../MTH_SUBWAY_CARS.htm
This link may also help-
https://ogrforum.com/...f-train-lines-by-set