I'm spec'ing a 2 zone system with a Yamaha RXA2050. Main zone is 5.1 with powered sub.
Zone 2 will use in ceiling speakers (maybe 2 pair), customer wants a subwoofer there too. Zone 2 line level out is not variable when using the built in amp so I'll need to use an amplified sub that accepts/converts speaker level.

Does the sub draw much current from the amp when being fed speaker level or is it converted to line level before it has a chance to draw power? My plan is to send full range speaker level from amp to the speakers. And run another 4 conductor in parallel to the subwoofer. Is the speaker level input of the sub high enough impedance that I don't need to worry about the parallel speaker/sub combo? My main concern is that I might use 2 pair of 8 ohm ceiling speakers. They'd be paralleled for a 4 ohm load. The AVR shows 6 ohm minimum - I'm pushing it but not worried, shouldn't be used at high levels. But will adding the sub in parallel gum up the works.

Should I use an impedance matching selector or am I safe enough? And, if the sub is not drawing much current, can I safely use 18/4? Alternatively, should I use a line level converter at the AVR and just run line level to the sub?
Thanks.

Something like this is all you need:
[Link: crutchfield.com]

The amp barely even sees an adapter like that as a load at all. Then you just need to run stereo audio to a powered sub. I've done it on Zone2 systems and it worked great. Even did it feeding a wireless sub adapter and that was fine as well.

Speaker level subwoofer inputs don't draw much power at all. I'd be amazed if...

OK, let me interrupt myself and ask: what's the brand and model of the subwoofer? We can call the manufacturer and find out what the input impedance at speaker level is! Now back to what I was writing:

...amazed if you'd have any problem using CAT5 wire for the speaker level inputs!

See, current is needed to drive a loudspeaker, that is, the driver itself. A subwoofer has an amplifier inside it that provides the power. All the sub needs to do is sample the speaker level voltage. Its input could very easily be 1K ohm, and in fact there's no real need for it to be lower than 1K.

You're running a wire just for the sub, which isn't a bad idea as it leaves future connections flexible. Run a wire that's as big as you think you might ever need, but don't worry about wire size with a subwoofer speaker level input.

I just looked up a random Velodyne model for reference. The Best Buy description for it was no help; it said "Inputs: None." The Velodyne website didn't have this either. It really will take a phone call to the manufacturer, at least for Velodyne. But still, you can't find out anything beyond theory without the brand and model number.

I called someone about the speaker level adapters a while ago - it might have been AudioControl - and they told me they have an impedance of something like 10K ohms and that the amp barely even notices that it's there

I would look for a subwoofer that has speaker level inputs as well as outputs. I would run all the speakers through the subwoofer and allow the sub to act as a crossover, to keep the low frequencies out of the small ceiling speakers.

Thanks, looks like the best solution. I can use any sub, not limited by whether or not it has speaker level inputs. I'll run line level like I would for any other sub. I'll throw an 18/4 in there too in case I do use a speaker level sub and then I don't need the extra converter.

The speaker level inputs on the subwoofer are basically speaker to line level adapters like the piece linked to the Crutchfield site. No need to add an external one if your subwoofer has speaker level inputs.