Well, great to see you guys thinking up all these options! Thank you. Here it goes:

"Control VS-100" is the Sonar V-Studio 100, an external soundcard. I use it for all music stuff and this used to work on BIAB 2010 (the last version I had before the current). Again, clicking the virtual keyboard yields sound in this setup.

I select GS Wavetable Synth and Route MIDI Thru to MIDI Driver -> no input from Impulse but sound from virtual keyboard

GS Wavetable Synth + VST off -> no input from Impulse but sound from virtual keyboard

Control VS-100 cannot work with VST off, since the soundcard doesn't have any soundbanks.

To cut a long story short, no input (visual or aural) from keyboard in any combination.

Moving on:
The Impulse is USB class-compliant. Novation provides a driver for so-called Automap features, but I haven't got it installed. No other programs are open while using BIAB.

Changing from ASIO to MME doesn't make any difference.

And finally, the MIDI Monitor shows no activity when inputting from the Impulse.

One final thing: when I had BIAB 2010 everything worked but with a different keyboard. So I set up the old keyboard in the configuration I used to have, but that, too, didn't register any input from the external keyboard. And of course, I also get no input from the EWI-USB. And both instruments work flawlessly in Sonar X2. Which leads me to think it must be a problem in BIAB.

So, not much further than we were. I'm going to put the question to Novation as well (have been hesitant about it, since I have more faith in forums than in support), but any suggestions are very welcome, naturally.

Thank you all very much!