Yr Egin, being built in Carmarthen by University of Wales Trinity St David, will be ready in late spring 2018.
University chiefs told the Welsh Affairs committee they hoped the site would ultimately be oversubscribed.
Vice-chancellor Medwin Hughes said he hoped Yr Egin would reach 60% capacity within the next two months but conceded it would need more companies on board.
"The £3m of upfront rent from S4C helps with cash flow for two to three years but we could need more than 60% capacity to break even," he told the committee on Monday.
As part of its contract with the University, S4C will also be paying £60,000 in annual service charges.
Brecon and Radnorshire Conservative MP Chris Davies told the committee there had been an "untidy smell around" the project and "a fog" surrounding the relationship between the university and the Welsh-language broadcaster.
Mr Hughes denied it, saying: "There has been a clear and consistent message between S4C and the University.
"As with any large agreement there are confidentiality agreements.  In the main, the engagement between S4C and the University has been presented in an appropriate manner."
MPs had summoned university leaders amid concern over a gap in funding gap for the project.
Earlier in March the Welsh Government committed £3m with after the University realised that the amount of European funding available to them would not be enough.
In February, First Minister Carwyn Jones told AMs that S4C promised that the move from Cardiff would be at no cost to the taxpayer.
The building which will be S4C's new headquarters has no other tenants signed up yet, MPs have been told.