What do I need to change to stay in Preset 2 while scrolling with the knob on the front of the Rack itself?

I believe you would need to transfer the MULTI LIBRARY Bank 2 into the Motif-Rack XS so that they can be selected just like the once already in the Rack XS (Bank 1). Transfer is one-at-time (recall/audition/store or not)

I believe the way it is intended to work is that these Multi Library setups are provided to Rack XS owners to match the 384 PERFORMANCES as programmed in the Motif XS keyboard synth. The Rack XS does not have a "Performance" mode so these MULTIS can be bulked into the edit buffer of the connected Motif Rack XS - and using the "Layer 1-4 Parts" function the first four Parts can be made to play from Midi input. Since MULTIS have contain the four Part setups you can transfer these keyboard Performance to any Multi location

With the Editor attached highlight a MULTI Name to send it to the current *Edit Buffer* of the Rack XS, audition it... If you want to keep it, press STORE and target a location in memory. if you do not STORE a it the data will be discarded when you move to the next program or you bulk in another setup. The first bank is pre loaded to the Rack XS, the others you will need to transfer, audition, and Store (if want to keep them in memory) one-at-a-time.

From the Owner's Manual (page 40):
When a computer is connected to the MOTIF-RACK XS and the MOTIF-RACK XS Editor has been installed, you can try the additional Multi programs provided in the MOTIF-RACK XS Editor. On the MOTIF-RACK XS Editor, the 384 (128 x 3 banks) Multi programs are provided. In the online status between the MOTIF- RACK XS Editor and instrument, select a Multi which is not included in the MOTIF-RACK XS on the MOTIF-RACK XS Editor then try playing the keyboard.

Thank you so much!
Your thoughts have given me a direction to move.