Someone needs to be the manager, but in your team's case, I don't think this is a full-time position. Hire another sr. dev and make one of them the manager. Ideally, the one who best fits being a manager and not necessarily the best programmer.
The manager needs to have the final decision where there is no concensus, so the person should be technically qualified. Evaluating the other programmers, the meetings, and fending off senior management is part of the job.
Suggested Reading: The Year Without Pants. Even a large software project (WordPress), can go without direct managers, but there are some tasks (no one wants to do/are very hard) or require integrating a large number of devs for the same task, can be very difficult without some central control.