2- the only opamp provided in DIP-8 format (which can be put into a socket, and so be replaced with another DIP-8 -or others, with adaptor- opamp without soldering) is LME49720NA, used as low pass filter (LPF). you can find it in stock pcb, and in upgrade #2. so these ones are the unique where you can roll LPF opamp without soldering, because there is a socket in the pcb for it. but beware, space (height) is limited, because the two pcbs of the player are very close. besides, these pcbs share the volume potentiometer type and outside connectors, so the outer shell is the same. the difference between stock and upgrade #2 is the I/V opamp: OP275 in stock, AD797 in the upgrade (i don't know about other electronic components). the rest of upgrades require a new shell, and you won't be able to roll opamps without soldering.
curiously, the mini A1 amplifier uses that opamp, AD797, so many of us have purchased stock zishan together with this amp (which also has other features than differentiate from the upgrades amp stage).