Can I use the "start" command with spaces in the path?
Use quotes like this:
start "" "Y:\foo bar\baz"
The start builtin command can be used to create new console windows, if you give it a console-based program (or nothing at all, in which case it starts the default cmd.exe shell).
If the first argument is quoted, start assumes it's the title for the new console window, so give it an empty title. The following argument will then be correctly interpreted as the command to run / file to open.
Put it in quotation marks like so:
start "" "Y:\xxx\dd sss\aaa\ccc"