Content for either event comes from a variety of sources, including product team/Engineering, technical marketing group and community members. The group that produced MMS is very much involved in the content curation / selection. You might know Ali - she was the event owner for MMS and is now a content owner at TechEd on a number of tracks, including PCIT / Datacenter / Azure and more. On those tracks - there are stakeholders who vet the content technically. Joey and I were stakeholders for Datacenter and we worked with Ali and team to produce the Datacenter track. We have allocation of slots to fill to make up the catalogue.
To be transparent - content and sessions that were made up for ALL events are created, refined and reused where appropriate. You won't see the exact same sessions on a topic delivered the same way by the same presenter at different conferences. We are constantly evolving and improving the content for each delivery. MMS content ends up in TechEd. TechEd content ended up in MMS. Same applies for Build or SharePoint or MEC. The content also ends up in 3rd party conferences where we speak. If you see Wally speak at MMS for an ILL - you'll see him deliver something similar at TechEd.
As for who runs either conference: MMS organizers hold key positions on the core TechEd team. The "executive sponsor" for MMS (CVP Brad Anderson) is a two time keynoter for TechEd and very much involved and invested. The events team that produces TechEd sits in my organization (Business Development and Evangelism) at Microsoft - same org as CH9.
@mfifer: thanks for the shout out on the speakers. You are correct - LOTs of familiar faces