repair or replace luxman preamp

find a local shop - here, they charge $45 to evaluate & give a repair estimate

Are you sure the lack of 'communication' is due to the pre, could it not be the remote?

First thing I would do is put a fresh set of batterys in the remote.

Re: remote control device. If new batteries don't work, it's possible that the sensor under the external buttons decided to give up the ghost.   You might find a replacement on Ebay.    Also, when you install new batteries, be sure to lightly bend out the contact spring.  Over the years, that spring can compress and lose contact with the battery terminals.

or maybe a universal remote could be programmed for your unit

or... replace the entire pre-amp