MERIDIAN DSP8000 What should I do?

Amazing speakers- congratulations on your find!  As Steve said, you may decide to keep them.  

From your question, it appears you have the older style 8000s, ones with the din and coaxial connections on the back.  You can source replacement cables on Ebay.  Reaching out to the HH Guide is also a good suggestion.  All of the manuals are available online.

You can PM if you would like accurate pricing regarding what you can expect to get if you choose to sell them.

Legacy  has the meridian logo lower while the later have the letter M there then 2009 to 2013 use a black soft dome and the 8000.2 use an aluminum tweeter from 2014 to current and the 8kse will have se in the sd on back and a be tweeter thats a darker grey than the.2. Like I said there's help on the hitchhikers forum, check 'em out. You may decide to keep them after you hear them.

Have you established what gen they are?

Go to hitchikers guide to Meridian forum. I bought a pair a few years ago and the guys on that site got me up and listening in no time, Freakin awesome find for the used prices. PM me with if you want to chat.

Meridian is it's own universe.  Now you know.