Thank you Dave; did not know about WinLIRC, interesting program. But that's the software end, what I need is the hardware unit to generate and IR-transmit the desired keystroke-combinations so that I can capture that on my universal learning remotes. But the compatible hardware listed on their webpage looks fruitful.

As for Mobile Mouse on a smartphone, yes, that would be a ready solution if 1) you already own a smartphone and 2) are the type who always carries your mobile phone on your person. I am decidedly neither, so in addition to whopping new Verizon or t-Mobile monthly fees, I'd need to buy 3 phones to provide the same at-hand convenience that my 3 venerable Sony remotes currently do; not a cheaper solution for me by a long shot :-). Plus unknown if the program can simultaneously control other IR-operated home theatre hardware -- cable box, receiver, etc.? -- essential for my setup.

But in typing all this up, came to realize that perhaps all I really need to generate the desired codes is simply an IR Windows keyboard, and capture the transmited signals onto the Sony remotes. A check on Amazon found this little unit, which looks like it could do that and serve good function on its own as well; I'll be considering that, but meanwhile am open to more suggestions; thanks folks.

Unisen iPazzPort KP-810-18R Wireless Keyboard and Touchpad with Learning Infrared (IR) Remote Control 2.4G RF