What's exactly your problem?
Do'nt know if helps, but I realize after trial and error that the VEH files for each car plays a fundamental role together with SRS files.
The "Classes" in VEH matches with "Vehicle Filter" in SRS. And, altought is says 'classes' in plural, in AMS just one class is allowed in VEH file. That's a main issue when porting from rFactor, where you might have multiple class definitions. The CLASSES are (as name suggests) the classes that you see in car-track selection screen (the third column of data).
1 - For instance, in rFactor you may have in VEH the following line to reference a LMP1 car in a WEC mod:
Classes="WEC 2017, LMP1" //a main 'WEC 2017' category, with a 'LMP1' subcategory.
In AMS, your VEH must be unique, for example:
Classes="WEC2017-LMP1"
This will match your SRS file like this:
Vehicle Filter=WEC2017-LMP1
2 - Following the example, a LMP2 car in rFactor would be:
Classes="WEC 2017, LMP2"
In AMS, your LMP2 VEH's must would be, for example:
Classes="WEC2017-LMP2" //notice that I create this name... it could be WEC16P2, for example.
Now, in my SRS file, since I want to have 2 categories, I would write:
Vehicle Filter=WEC2017-LMP1 WEC2017-LMP2 //notice the space between the two classes
3 - Now, the CATEGORY in VEH file is used in AMS to create the tree folder structure for car selection.
In the VEH that describes the Toyota LMP1, I'd write the following:
Category="WEC 2017, LMP1, Toyota T050 Hybrid"
Team="Toyota Gazoo Racing"
Driver="#7 Kamui Kobayashi"
That will be shown in car-track selection (in first column) like:
WEC-2017
|-> LMP1
| ----> Toyota T050 Hybrid
|--------> Toyota Gazoo Racing
|------------> #7 Kamui Kobayashi
Please take a look at my skinpack for reference, where I've created a multi-class series for AMS:
http://www.racedepartment.com/downloads/endurance-brasil-mr18-and-mcr-2000.13338/