I kinda lost you through some of that. unfourtionately my electronics knowledge is a little shaky.
Well, you're in a great place to start learning, I can assure you that.
What parts are confusing to you? I'm happy to explain things as best as I can...
Okay, buffering the outputs of the differential pairs formed by Q1&Q3, and Q2 and Q4 is not the most crucial thing here, since output impedance is already low.
To provide your differential with a current source, remove those 8.2K resistors, R12 and R13, and substitute a current source instead--try using a pair of diodes in series--that runs from the V+ to the emitters of Q1/Q3, and Q2/Q4.
Since we're using diodes, we want to connect the positive end (the anode) to the most positive voltage, and the cathode (the band) will point to the less positive voltage.
Connect them like this: anode of diode 1 to V+, cathode of diode 1 to anode of diode 2, cathode of diode 2 to emitters of Q1/Q3. Do the same thing for Q2/Q4.
Theoretically speaking, the two diodes will appear as a very large resistor to the emitters of those particular transistors, and should increase CMRR to around 100dB IIRC.
Also, what type of PNP transistors are Q1-Q4? Maybe there's a lower noise sub available...