HDMI rather than dongles
Thank you for your directions, Pepe7, which I will follow up once I understand how to deal with my iMac's HDMI shortcomings. HDMI would seem in theory to be the next simplest way, after an android dongle, of satisfying my need to manage my HDTV input remotely from my computer.
However, my Early 2009 iMac has a Mini Display Port, rather than an HDMI port, that transmits video but not audio signals. I've been trawling the forums for solutions, only to be made aware of more associated problems.
Apple, at http://support.apple.com/kb/HT424, names three examples of "third party Mini DisplayPort to HDMI adapters that conform to the VESA DisplayPort Dual-Mode Standars", that will deal with this. However, this is disputed by 'eww', posting on 23/09/10 at https://discussions.apple.com/thread/2590139?start=0&tstart=0, who reckons that these adapters, connecting to the Mini DisplayPort alone, will find no audio signal there to transmit, and recommends three other adapters that combine the video from the Mini DisplayPort and the audio from either a headphone port or a USB port.
Then, 'SlugBlanket', posting on 12/09/11 at https://discussions.apple.com/thread/2639905?start=0&tstart=0, points out that these are not plug-and-play solutions and that care must be taken to appropriately modify one's video and audio System Preferences, and the MIDI setup utility in Audio MIDI Setup.
As if this wasn't enough, other posts elsewhere refer to the existence of associated software bugs in OSX . . .
Assuming all of this (and doubtless more) can be overcome, the possibility of 'wirelessly' connecting my computer and HDTV, via my domestic power circuit, using Powerline Network Adapter Kits, beckons. But again, the Devil appears in the detail. OK for Ethernet connections, but not so simple or inexpensive for HDMI . . .
Finally, my apologies for having taken so long acknowledging your helpful post, but I'm finding myself going round in circles trying to get to grips with all of this.
In the meantime, I would appreciate any further advice that you or anyone else might like to offer.