Ok, so I looked into getting a Macbook and it turns out Homepods can't be connected to it either (as desktop speakers)! Can you imagine? Technically they can be, but there will be half a second delay, rendering them useless for video calls, and Apple has no plans to fix it. Same story with Google Home Max speakers, which I also considered, and which have 3.5mm analog inputs. Just got off the phone with a Google support rep, and he told me the only way is to do Chromecast, which will also have a delay (and might have other issues as well).
So I think I will go with S350DB - the bass is ported, and listening to this test:
looks like it reaches down to about 42Hz (and surprisingly there's some audible rumble at around 25Hz), but that's with bass turned up all the way. I also considered S360DB, which has a wireless sub, but from reviews it seems like people don't like its harsh trebles (it has different tweeters), and I'm not sure they are intended to be listened to at close range (on a desk). S350DB is. I'm not sure yet where I would put the sub, it's not that large (compared to S730), so I might even be able to fit it on the desk.
Regarding speaker placement on desk - there are two options: below the monitors, and above the monitors on stands. The first option is the easiest, but not ideal - the tweeters would be way below ear level, and the speakers would have to be horizontal, not sure how would that affect the sound (all those things like soundstage, etc). The second option is less visually pleasing, but probably better from the acoustic point of view.
@PaganDL I'm confused about those Dalfred stools - are you suggesting placing them onto a desk? They seem way too big for that. I'm thinking more of something like
https://www.amazon.com/VIVO-Monitor-Adjustable-Mounting-STAND-V004/dp/B009S7IDJQ (quad monitor arm, screwing some larger plates onto the two vesa holders. Or, as you suggested, mounting each speaker separately on something like this:
https://www.amazon.com/VIVO-Single-Laptop-Notebook-Mount/dp/B00CM9NG1W which seems to be a visually cleaner approach, not sure yet.
Now that I'm thinking about mounting the speakers above the monitors - should I place them vertically or horizontally? Or maybe I should even consider using 2.0 system since the space is no longer limited to what has to fit below the monitors?