Status report:
* Trying to connect USB - USB didn't work, Windows didn't recognize the G68. Perhaps installing a driver or something would fix that problem.
* Discovering the mentioned Options allowed to change from USB1 to COM3. That in itself didn't help.
* Tried lowering transmission speed to 2400. Still no go.
*
Raising the speed to 4800 - and connection established!

Now that I know I can get config changes stored I will go through and change the last details, for instance the new TV has no analogue sound out but a toslink instead. The cable I had lying in "storage" is too short so if I don't have another one lying I'' need to buy one (nice if just watching a TV program and want better sound than the built-in speakers even though that model is unusually good for a TV). I also will check the BD player manual, I believe I remember it's "smart" so that one of the two HDMI outputs is soundless so you connect that to the TV and the other to the HD621 and you don't need to turn off the sound of the TV when watching a BD.
BTW, is there a problem having the cable connected to the maintenance RS-232 port all the time? It's a bit of a hassle getting at the back of the system.