I was wondering if there was any advantage or point to matching the CSS ZTX450 across channels in the Aleph amps? Would this improve matching of current draw or bias between channels? In the mini-A schematic the parts in question are q4 and q5..
In the schematic you show, Q4 acts as a safety valve to limit the amp's max output current in the event that the outputs are shorted. Q4 doesn't take an active role in the circuit unless an upset condition occurs.
Therefore, you won't find any benefit in matching Q4 to Q5. Likewise, you wouldn't find any benefit in matching Q4 in one channel to Q 4 in the other channel.
There can be a benefit to matching Q5 left channel to Q5 right channel in order to get better matching between the current response of the Aleph constant current sources. However, most builders have included potentiometers in the Aleph CCS that allows us to trim the current response and bias level. These adjustments are discussed in detail in Nelson's Zen series of articles.