Yes, I will say you modified it and that was not the way Cox provided it to you. They didn't advertise and sell you external storage capability. If you could show me any advertising or marketing about external storage that would be great. The only known mention of the External storage was from a copy-pasted blurb on the internet in one of the Cox markets, that came from from the manufacturer back when it was SA using SARA software when the 8300 was first released (from the original SA user manual). We still don't use the USB and Ethernet ports, although Cox has mentioned that they may utilize the network functions for media support in future versions of software once DRM is accepted.
As for family use, we have and use three DVR's and we now use OnDemand more and more for most of the programming because there is no need to bother setting up a recording, worrying about conflicts, or network issues causing problems. I do question WHY would you attempt to add storage before it was even necessary and not use OnDemand for some of the family members. With only two tuners and a high use of 8 hours of recording a day, it would still take two weeks to fill the existing drive.
For the record, I DO use an external drive(s) and have upgrading DVR hard drives since the day DVR's were offered by Cox in my market (beta tester) and have been using DVR's and modifying them even before Tivo existed with ReplayTV in the 90's. I have sold and installed dozens of the 500GB WD DVR expanders in several markets and MSO's for customers using the 8300, and then the 8240 series of DVRs with the explicit information that it was a non-supported feature that we were taking advantage of and that at any time the feature may not work and they could lose access to anything stored on those drives.
Note that these are my opinions and that I have been reading and catching up on various forums while enjoying, now it seems, several frosty beverages while my dinner was forgotten and waiting to be reheated.