Just FYI the classic version is not compatible with max. It won't be usable in Max. This is due to the changes in the DBO format for max(Which is now a closed format) and the texture assignments. If you were to import a model from classic it would have messed up texture assignments due to being multi textured, this can't be manually fixed without the source files or if you have software to manually edit the original classic files.
There is also a planned series of themed underground packs that will have parts that will connect various DLCs together, with two yet unreleased DLCs. The sewer will connect with a unreleased pack, that will connect to the secret bunker which will connect to another unreleased pack. All future DLCs in this series and author will follow a similar pattern of being interconnected in some form or another.
Also worth noting if you have the TGC version it is exactly the same you don't need the steam, version. Only difference is updated naming conventions as required by TGC.
Win10 Pro 64bit----Intel i7 4770k @ 3.5GHZ----GTX 1660 6gig----16gig ram