Either you go with the first suggestions of you hire a design firm that will be sensitive to what you like about the raw space. We often approach projects that have great vibe and appeal in the raw space and discuss how to "keep" that vibe with the clients, even though we are going to build an entire isolations shell inside the building.
THere are many things we do including use materials that compliment the existing demising conditions, re-introduce brick veneers, stone walls, etc inside live rooms. It's all about maintaning the vibe. The sound can be as live (in a larger room) as you want it to be... The fact of the matter is, it would get quite 'old' trying to record in the warehouse, factory, whatever, WITHOUT some type of 'studio' installations, like iso booth, a control room, you know... the little things...
Seriously, we approach each project as a unique challenge to create something from the raw space whether it's a church on a lake, or a loft looking over Brooklyn and the East River, that compliments the location and serves the clients' needs... and hopefully works within the target budget. If all these variables are compatible with eachother, that's when we have a winning project.