Do any of the third-party players support 1.04 (i.e., the Dell boxes), and can run with the HSX-109 as their server?

Certainly some of the replacement players can use the original server as their server. Does the HSX-109 implement the same protocol? If so, I don't see any reason why they wouldn't work against it as well as the software.

And they definitely work on the Dell units.

I'm thinking of tRio, specifically, although it requires some additional stuff be run on another computer, so it may not meet your requirements, even though it can point at the original server software (in addition to jreceiver).