Hi,
I ended up with a used Flex 5100, and it turned out to be a really good choice.
The USB to DB9 to Null Modem cable combo keeps the Elecraft KPA500 happy, and both do MARS frequencies exceedingly well.
Given that Flex Radios can or will allow another flex user to use my radio (and vice versa) over IP, the only issue remaining is that the distant user, IP-using my radio, will not be able to switch the Elecraft KPA500 linear between Standby and Operate until I come up with a work-around.
My inclination (worst case) will be to build a solenoid that literally, and gently, presses the Elecraft button to switch it between standby and operate. Such a button will have to be operated over IP by the distant operator. Further, i would probably have to set up an IP camera on the green and yellow LEDs so the distant operator knows whether the KPA500 is in a given mode. Camera needs to be positioned so the distant operator can see the SWR status of the amp. What i do not want to do is remove the KPA500 front panel and go after it with a soldering iron (bye bye warranty).
I posted a query on the Elecraft listserv list, and it didnt even show up in the listserv digest
My 2 cents worth; and I have no fiduciary relationship with Flex, is that I'll take the flex over the top of the line Icom/Yaesu/Kenwood. The only time I even look at the Flex radio is to press the on off button. It's out of sight and out of the way. The only way I would go beyond a Flex radio would be for Barrett 2090 or 2050.
VR/Jack