Yea! First poster that has mentioned Sound Board! Bonus points.
I have built music rooms in $10 Mill. + houses, where sound had to be absorbed, period.
It has been many years granted, technology has changed and new innovations in sound proofing have developed.
I am not currently active in building, so I can only share my older technology experiences.
We started with offset stud wall construction, room within a room style. The interior wall studs did not touch the exterior wall studs (nor the top/bottom plates), interior wall studs were centered in the gap of the exterior wall studs. On the interior wall we screwed 5/8" soundboard on the walls and ceiling, then had a company come in and blow fire retardant cellulose between the offset wall / ceiling spaces. Hole saw plugs were glued back in place. 5/8" sheetrock was then installed over the Sound Board. Wiring was completed and the 2 1/2" solid Mahogany door was hung. Similar to your design lighting was provided by torchieres and desk lamps.
That room was ~ 16'x30', I don't remember the dimensions exactly, but it was QUIET, inside and out.
I think it is easy to become overly focused on technology and the "latest and greatest" whatever the subject, and loose sight of why it works. Dead air space with sound absorption materials, the more the better. Decoupled from exterior structural members. KISS.
First off, MDF is NOT Multiple Density Fiberboard. It's Medium Density Fiberboard. There is also HDF, which is ungodly heavy and hernia inducing stuff.
Perhaps the poster was thinking of OSB? Oriented Strand Board.
Secondly, Don't all condoms come with a hole in one end? Otherwise it's a sealed tube. JK. Just pointing it out.
You had ceiling height to spare, should have gone with 2x6 instead of 2x4s. 2x4 just barely meet the load/span calculation tables for a 16" O/C 5lbs dead load with a deflection of //240. That said, 2x4s will work, don't forget to block them.
If you cut holes in the ceiling for speakers you will mitigate the sound proofing the ceiling affords, speakers send sound in both directions. Also the dispersant patterns of most in ceiling speakers will be "sweet spot" truncated.
Cinder block walls must be treated (I'm sure you know this) for sound reflections. Their mass is outstanding for sound deadening from the outside. If any portions of this room are below grade, you may have issues later with moisture penetration through the block wall, between the block and the false wall. Keep this in mind as you build.
Think about exterior drainage solutions away from the building.
Provide plenty of air circulation, especially air exchange. A sealed room will become stale, hot and humid without fresh air circulation.
Please post pictures.
General Contractor 35+ years
Mold Remediation Certified