The locomotive from that starter set is a BR 81. Delta locomotives can be operated in a Digital Environment as they the simplest form of Maerklin Digital. What controller are you going to use, the 6021, Mobile or Central Station?

There are three BR 81s that match your basic locomotive Model Nos. 30321, 30322, 36320. The 30321 is the Hobby model no decoder but can be upgraded to have a digital decoder installed, the 30322 has the Delta decoder and the 36320 has the fx decoder for use with the 6021 Control.

Here are parts breakdown from Maerklin's web site:

http://www.maerklin.de/s....php?artikelnummer=30322

http://www.maerklin.de/s....php?artikelnummer=36320

Looks like you could use the 60921 High Efficiency Propulsion kit. You should contact your Maerklin dealer and find out which MFX decoder and propulsion system should be used for this locomotive. If you do not have experience doing conversions let your dealer do the service.

Check the brushes of your motor: if it has one copper brush and one coal brush side by side then it's a flat collector motor; if it has two coal brushes in opposite positions (as shown in the 30322 drawing) then it's a drum collector motor (DCM) and set 60921 will fit.

My BR 81 is from a starter set (but I don't know which coz I bought it separately a few years ago) and it has a flat collector motor (FCM).
Because there are FCMs of different sizes (called SFCM (small) and LFCM (large)), there are different sets to upgrade them. If you have a loco with FCM we still have to determine its size.

I knew you would get the answer here !