David Looser wrote:

The odds that they will be quads is about zero, since headphone
drivers are typically used in pairs.

Agreed. I know of no quad op-amps that will do the job. I think Tony
should accept that he will need a separate h/phone amp chip.

All comments noted. Thanks.

The *only* problem with the LM324 in this application is the crossover
distortion. It drives low-z headphones fine. So, I'll try plugging in a
TL074 and see what happens before looking to a purpose designed hadphone
driver.