Questions about Qtractor

forgive me if these are stupid questions...

as they say, no question is stupid, answers might :)

1. Is there a way to send a signal, from a track or a bus, to multiple other tracks or buses so they can be processed further independently? It seems like when I use an Aux Send, it "steals" the signal at that point and sends it to the destination, but removes it from further processing in that track.

exactly the purpose of an "Aux Send": however you can only route to existing output buses; tracks however are out of the question; and it should not "steal" in any way possible unless it's not activated or the send-gain is set to 0 (silent) or worse, the aux-send bus is set to "(none)".

2. I'm just not understanding the difference between using an Aux Send and an Insert. They both create JACK ports. I know that in the case of an Aux Send, there's only output, no input, but other than that, how else do they differ? Oh...inserts do a send/return externally without involving any buses. Does the returned signal then proceed through the rest of the processing for that track and then get sent to the track's output bus?

an Aux-Send is a means to route-fork the signal at the insertion point: the forked signal is routed to the designated output bus; the main signal goes through to the next plugin in chain and/or designated track/bus output.

an Insert is aka. a send/return insertion point: it makes possible to connect to and from external JACK (audio) or ALSA (MIDI) applications, with the provided Insert output (send) and input (return) ports respectively.

3. Is there any reason why you can't take the sent output, and instead of processing it externally, just connect it to some other Qtractor JACK input port, maybe one that was created as an input bus?

yes there is: internal signal processing is always in the so called "forward" direction: input bus -> tracks -> output buses; that's why you can only have aux-sends to output-buses and nothing else that would violate the "forward-only" rule.

4. When you create an Aux Send, you can route it to bus "(none)". What the heck...what happens then, and why would you want to do this?

yes, you're probably right, there's no reason for anyone to do it intentionally, but note that if you remove an existing output bus, then most probably all the aux-sends that refer to it then will make it to "(none)" as a stop gap.

5. When you create an Aux Send, you have to select a Send Bus, but none of the output or duplex buses I've defined show up in the dropdown? Why not?

all eligible output buses for an aux-send must match exactly the number of channels as the current output bus that is assigned to the track, simple as that.

6. What is the "Direct Access" dropdown in the Aux Send dialog? Does it have something to do with connecting the indicated control to some hardware device?

no, it's just for you to choose which parameter to show and access as a tiny slider on the plugin-chain list; try it out :)

7. Is there something special about the Master bus?

nothing but the first bus where all things get connected by default; for instance MIDI tracks with instrument plugins that produce an audio signal gets automatically routed to the first existing audio output bus (which is often named Master Out) but you can always change that anyhow :)

hth.
cheers

ps. these are all fairly basic questions that should be implied in the https://qtractor.org/doc, especially in section 4.8.3 Buses