Yes I think you have it. The HL2 skeleton rigs and the CS:S ones are similar but NOT the same... and even one extra bone I think would mess everything up.
If you want to use the CS:S animations; decompile one of the T or CT models, import into max (using wunderboys importer) and delete the mesh so you have just the skeleton. Now take your model and add a skin modifier with the skeleton from the decompiled model. Weight your model the way you want. Then when you recompile just add to your .qc the following
$includemodel "player/cs_player_shared.mdl"
$includemodel "player/ak_anims_ct.mdl" OR $includemodel "player/ak_anims_t.mdl" (depending whether you used CT or T model)
If you want to use the HL2DM animations then you must do the same with a charater from that game instead.
If you want to use the CS:S animations; decompile one of the T or CT models, import into max (using wunderboys importer) and delete the mesh so you have just the skeleton. Now take your model and add a skin modifier with the skeleton from the decompiled model. Weight your model the way you want. Then when you recompile just add to your .qc the following
$includemodel "player/cs_player_shared.mdl"
$includemodel "player/ak_anims_ct.mdl" OR $includemodel "player/ak_anims_t.mdl" (depending whether you used CT or T model)
If you want to use the HL2DM animations then you must do the same with a charater from that game instead.