Update:
Have since received the proper monoblock and the Neli has no problem reconizing it. I'm using a simple coax switch with one cable to my TV and the other to the Neli. Not the best solution I know, but one that fits my current financial situation. I realize a decent permanent solution would require a dedicated twin LNB for Astra alone, but couldn't be bothered right now with all the extra hassle.
One downside of the manual switch option is that the Neli sometimes loses its connection with Astra after switching back and forth, in which case it needs to reboot, sometimes taking up to two minutes to readjust.
It may be that this is a function of the last channel watched on my TV tuner before switching to the Neli. This was the case on my old Optex equipped with an IF OUT jack. Only when I selected a certan channel before turning on the Optex would its connection to Astra occur automatically. Strangely enough, I had to tune my TV tuner to a Hotbird station for the Optex to immediately recognize Astra. No only that, not all Hotbird stations. I'm not sure which ones worked here, but I always used the Iranian stations "AVA Movie" or "Movie1", perhaps something to do with the polarization?
I should add that I always unplug the entire TV/receiver system every night via a floor switch, so this may also have something to do the Neli's function.