Yo Barry! I identify 2 questions:
1. How do I make my concrete box sound better?
2. What's the weakest part of my signal chain, and how would you recommend I improve it?
My answer to number 1 is- check Ethan Winer, and build some bass traps. Install them in the corners, and then make the room *softer*. We started at a bargain basement joint and bought cheap rectangular sleeping bags and hung them on the walls. We've upgraded since, but they worked rather well. Just build a padded room. To the people who think foam doesn't work, a cut up wrestling mat does. Sometimes you can get some worn out sections of ensolite from a high school wrestling team. Do a search on "rock wool". Hell, even hanging a velvet Elvis on a concrete wall is better than nothing.
My answer to number 2 is- you need some mics. There are thousands, ranging from $20 to over $10,000. As far as cheap mics, my favorites include Marshall Electronics (MXL) V67G, AKG C2000B (my personal dark horse favorite), B.L.U.E. Bluebird, and CAD M179. Any good condenser will showcase how much your concrete box sucks. The good news is- concrete has a lot of mass, and once you soften the surface, that mass will give you good isolation.-Richie