Great! Thanks for the confirmation. Found the 4072 just after I posted and looking at the schematic, Rane stated that an equivalent substitute could be the TL072. I did some research and discovered the OPA2134 (an upgrade for the TL072) as you have suggested. The specs show improved noise and slew rate and though the 4072 sheet doesn't specify THD, I suspect it will be better.
There are four of them as line amps for the 4 inputs (dual-mono unbal). I found 5 for $14US from a US vendor but the picture and description show them as "original BB" with the BB imprint on the chip. Do these earlier chips differ from the later TI units in their specs? If so, should I be looking for these later TI chips?