Air Carrier Captain reported a 'dirty socks' odor of increasing intensity during departure taxi. After receiving a flight attendant call regarding the fumes the Captain requested a Ground return where Maintenance assigned an aircraft swap.

Narrative

Apu was already on MEL due to fumes event the prior evening. Coincidentally I was also on that same flight commuting to work on flight from ZZZ1. We started engine #2 at the Gate using air start procedures. We pushed back from Gate and started taxi out to Runway XX. On the taxi we used the crossbleed start procedures to start engine #1. During the clean up procedures after the crossbleed start the First Officer turned the #1 engine bleed back on. Almost immediately we could start to smell the dirty sock smell that gradually increased in intensity. By the time we were halfway to Runway XX inflight had called up front to let us know the fumes were bad in the Cabin. We immediately told Ground we needed to return to the Gate. We then ran the odor isolation procedure in the Flight Crew Operations Manual and decided to shut down engine #1 because we thought that engine was the source of the fumes. The First Officer opened his sliding window; and the Cockpit odor diminished quickly. Three calls were made to inflight to gauge the intensity of the fumes in the back. The fumes slowly subsided in the Cabin. We had to wait 20 minutes for a Gate but returned where the aircraft was removed from service. We swapped aircraft and continued flight.