These documents have more appropriate information:
Gypsum Board Walls: Transmission Loss Data
By Halliwell, R.E.; Nightingale, T.R.T.; Warnock, A.C.C.; Birta, J.A.http://www.nrc-cnrc.gc.ca/obj/irc/do...r761/ir761.pdf
Controlling Interoffice Sound Transmission Through a Suspended Ceiling
by R.E. Halliwell and J.D. Quirthttp://www.nrc-cnrc.gc.ca/obj/irc/do.../nrcc33097.pdf
...along with those covering flanking. Additional information is available at www.soundproofingcompany.com
When you read material, or speak with contractors/consultants, any information or discussion with only STC values or STC classes are not appropriate to your application. You'd need to pay attention to transmission loss values (TL) or look for the more appropriate NR or NC ratings where available. The lowest frequency evaluated for an STC class rating is the 1/3 octave centered at 125Hz. This is value is completely not relevant to audio applications. The STC rating system was developed as a metric to evaluate sound isolation constructs to mitigate transfer of human speech and office equipment (typewriters, copiers, telephones ... usual and customary human activities.)
In audio applications we must deal with frequencies down as low as 20Hz, if not lower. Indeed, a barrier can be constructed with a high STC rating by engineering that barrier to lower its resonance frequency to a value less than 125Hz. For the sake of example only, let's say we build a barrier (wall) with a resonance frequency of 80Hz. That barrier would have a high STC value yet be virtually transparent to your subwoofer at 80Hz. A disappointing result.
Typically, in audio listening environments, the goal is to lower the noise floor in the room to 20dB NR or NC. Considering a quiet home has a noise floor in the 33 to 35dB range which is not an overwhelming task. However, what you are seeking to do is quite different. The dynamic range in audio playback is 22dB to 115dB. So, in essence, you want to reduce the transmission of sound out of your space from 115dB down to below 33 to 35dB ... a big challenge. In practice the generally acceptable practice is to reduce sound transmission out of the room to the extent you do not raise the noise floor in an adjacent space by more than 3dB. That is a big challenge and not an inexpensive one particularly in an already finished space.
In the end, you need to decide just how big an increase in sound level is acceptable outside the room and what your budget is to make this happen. I should also note that whilst 115dB is a big number, many will find it more than acceptable to base their sound abatement on a reduction of about 50dB.
That, btw, is not 50dB across the board. NR, NC, and STC ratings account for human hearing sensitivity at different frequencies.
Basically, decide what you're willing to accept and build to that goal; but, as has been said before, any small gaps, oversights, and shortcuts could render all your other work moot. Commonly those problematic flanking paths include electrical boxes, light fixtures, and HVAC penetrations through your sound isolation barrier.