Is it correct, that when running an 2x10 (8 ohm) cabinet with a 4x10 (4 ohm) from the same channel of an amp, all speakers will see the same amount of watts? (Provided amp is safe to run at 2.67 ohms, of course) Thinking about a modular setup: 2x10 for small, 4x10 for medium and both together for large gigs. Thanks!

This is true when all the drivers are the same. For the 2x10, this would be two 16-ohm drivers in parallel. For the 4x10, the same 16-ohm drivers all in parallel. Each driver will see the same voltage. Watts is a power number calculated by the voltage squared, divided by the total impedance, as E² / R. This is a very flexible arrangement and will work well for you. The trick is using 16-ohm drivers (I assume G-K?), which allows for the all parallel wiring scheme.

nice idea. i fooled around with that as well but i did not find an amp that was within my budget and powerful enough and 2 ohms stable. There are not too many of those, and i wanted class D or at least something smaller and lighter than my old peavey mk IV that can do 2 ohms. I figured, there is no use in having the possibility to go small and just take the 2x10 when you have to haul a 90lbs tube head anyways. I finally settled on 2x12 and 2x12. one's enough for smaller gigs and 2 are enough for anything short of bringing down the house.

i don't know why the companies don't sell this idea! using all matching 8Ω drivers we could have an 8Ω 4x10 and a "matching" 2x10 that switched between 16Ω (to stack on the 4x10) and 4Ω for use by itself. 2 tens for little gigs, 4 for regular rock gigs, and all 6 for big outdoor shows or whatever, running at an amp-friendly 5.3Ω.

And going farther back, it's a trickle-down from JBL. G-K kept that great idea alive by using the 32-ohm, 16-ohm and 8-ohm Paragon drivers for their various cabs. The advantages to all-parallel wiring are substantial. There appears to be a small efficiency gain from the higher impedance drivers as well.

Pretty much à propos, I guess I could submit my little suggestions in a thread about adding an SWR Goliath Jr. II to a Goliath II, driven by a Crown stereo power amp, for your review. 1, and especially 2 and 3. I tried to do the math as accurately as I can, but might well have overlooked something and wouldn't want the OP nor anybody else's cabs, amps or both on my conscience...

The drivers don't necessarily have to be 16 OHM - You can Wire 4 Ohm Drivers in Series for the 210 cab and wire the 410 cab in Series-Parallel and still achieve the same desired output of 8 OHM for the 210 and 4 OHM for the 410 resulting in the 2.67 OHM combined.