Thank you, Forum members, for each of your responses and suggestions...
In the meantime, since Ido have a separate home theatre system with its own sub. I tried interchanging the subs in each system. I confirmed that each sub does work in the corresponding system. However, the sub from the home theatre system is of considerably lesser quality, so I do wish to continue to work towards a more satisfactory solution.
So, back to square one... the Paradigm Seismic 10 sub works but not when directly connected to the Ayre preamp.
Subject to receiving any additional opinions, I think that the next solutions to be tried are (1) adding some resistance to the preamp-sub connection, or (2) trying to connect the sub to the LFT-8 speakers.
I will advise as to what success, I achieve.
I can advise that I am still waiting for a response to my e-mail from Ayre (12 days and counting) and have sent an e-mail inquiry to Paradigm (3 days ago).
Thanks again for all of your good advice,
Peter