It was both an electrical adjustment and a firmware upgrade to version 13. I had it performed a year ago. It even says in the original spiff space faq:
161-6: This seems to be a hardware problem with the Sony DVR and a CC. The only fix at this time is to send the DVR back to Sony for a electrical modification and firmware update.
And it's not just these DVRs there is a long list of other products by Sony and others that would need a firmware update and tuning adapter. And according to the Cable Labs website, they all are compatible with the tuning adapter specs (TRIF). The list can be found here:
http://www.cablelabs.com/udcp/downloads/OC_PNP.pdfSo I'm still curious as to why anyone thinks a firmware update is impossible. I'd be interested more in facts than speculation, though.