When you enumerate a table it will enumerate over all sym columns. There is no need to specify account and sym as they will be picked up on. This will generate an index as such of all symbols in the table between all sym columns.
You can as you suggested partition a table with multiple sym files. Though this is necessary only in exceptional circumstances, for instance if you're concerned about bloating. It is also worth noting that unless you are capturing hundreds of thousands of positions, a splayed table may suffice for your needs.