AMG Wealth Advisors, a subsidiary of Affiliated Managers Group, which has been making investments in advisory firms in recent years, has kicked off 2015 with a sizable deal in the RIA space.The firm announced on Tuesday that it was taking a majority stake in Baker Street Advisors, a San Francisco-based investment adviser that had $5.2 billion in assets under management, according to SEC filings from last year. It now has $6 billion in assets under administration, according to a press release. (More: $1B firm merges under consolidation pressures)