Because of the nature of the eXStatA design, the input JFETs must be Idss matched to within 10%. None of the other active devices in either the power supply or the amps need matching, including the tubes. Tubes, however, should be in good operating condition. Using the parts in the BoM or same spec items will ensure that the passive components are matched as well as they need to be.
JFET matching is a simple procedure that only needs a 12VDC supply and a DMM set on 30mA scale. Use this schematic:
Match the Idss to within 10% for a quad of JFETs, two fets per channel. The earlier builders have discovered that it takes about 20 fets to get one or two good quads.
DO NOT use JFETs with ldss less than 10mA.