Ken Wilson schrieb:

Whew. I do not know what I was thinking.How can I sell such a nice
set. Thank goodness no has said they want the 525.

So cancel your offer right NOW! :-)
Everybody must have been thinking you were flooded with offers.....

Just sell the optional boards separately or put them on ebay.
I bet you will get a least 400US$ for the "naked" 525 easily as it still
comes with the additional superb 1khz filter.
I was very lucky when I got the chance to get the RS232-board some years
ago from a nice guy in the US for US$100 with the cable and a nice DOS
program to remote control the 525. There are several programs out there
since then....