You're going to want another LSD.
You're going to want a diff out of an E34 (non M5/540 as those are much different) or one of the smaller ones out of an E32 (like the 735). Don't think the E36 diffs are interchangeable.
As far as which ratio to go with? Depends on how much you want your gas mileage to decrease. But the 3.73 should be your best bet for a good balance of improved acceleration/gas mileage loss.
Auto/manual doesn't matter in the build of the diff. Only difference between them will be the ratios.
Reminds me I need to figure out which ratio I've got in my car now to figure out if the 3.91 LSD I picked up is too low. Couldn't pass up a diff like that for $200 though...
Cosmos Black/Black 1995 540iA M-Sport
BMW Individual Exclusive Edition, 1 of 65 total, 9/25/95 Build