"An authoritative source"
tells me you can easily fit 10 or even 12 musicians into the Musician's Gallery - although issues of both HIP, and - more persuasively - budget have dictated that this number have but rarely been gathered there. However, I wouldn't greatly like to be involved in taking any large instruments (harpsichords, chamber organs etc) up the tiny wooden staircase that leads there. I dare say they could probably be humped up there with determined effort, which would theoretically make it possible to stage Purcell pieces there. However, I doubt this chimes with the artistic vision of Mr Drumgoole.
There is, however, a second auditorium within the Globe's set-up - but it's never been put into commission. The original plan included a replica of a Jacobean indoor theatre. Whether the Globe have plans to open it (it was shelved in the "Phase One" plans, in the interests of getting the main house open to schedule and to budget) I don't know - or whether the space is still available in that piece of prime real-estate down there? (Quite apart from the niceties of historic dramatic practice, the idea was to give the Company somewhere to perform in wintertime). It was being spoken of as a serious and practicable auditorium as recently as last year to my certain knowledge... there'd been a projected rather glamorous production of Monteverdi's L'ORFEO there for the 400th anniversary of the (1607) piece, and moreover it was scheduled to tour all over the place (including, ehem, Moscow). However, for reasons to which I wasn't privy this never happened, and the project fell into an Underworld of its very own
senza ogni speranza.
Who knows - maybe THE BURIAL AT THEBES is scheduled for the second stage? I rather doubt it - the money needed to get it to performing condition is enormously out of the reach of a company struggling to balance the books as it is