Should spatial perception x what you describe differ for, say, bass in outdoor setups (I am sorry - I realize this is slightly tangential from the OP query)?

@benanders Outdoors we can sort out where bass notes come from. But in most rooms indoors we cannot since it takes a few iterations of the bass note to pass our ears before we can know what bass note it is. By that time (in most rooms) the bass has bounced off of several walls and so is 100% reverberant.

is this statement meant to rule out bass as being important to listener perception of soundstage?

@benanders Yes. Bass (20Hz to about 150Hz) is important if you want to get the tonality right but it has little to do with imaging and sound stage- the lower the frequency the more this is true. Below 80Hz in most listener's rooms the bass is 100% reverberant (which is why subwoofers don't have to be in the same location as the main speakers if crossed over below 80Hz).

You can try a simple experiment to show how this is so. If you use midrange drivers and tweeters as speakers you'll find they can image nicely, but if you use only woofers that are rolled off at a normal crossover point you'll find the image very indistinct or non-existent, depending on the woofer.

I have a pair of Thiel CS6 speakers that dip to around 2 ohms in part of the frequency spectrum. I run them with a Krell KSA 300S that doubles its power down to one ohm (300 watts @ 8 ohms, 2400 watts @ 1 ohm). When I took the amp in for recapping I tried hooking up my Onkyo A/V receiver to the Thiels. The results were laughable. The Onkyo sounded like an AM radio. The soundstage was flat as a pancake. I figured there would be a difference but I had no idea it would be that dramatic.

@8th-note Your conclusion might not be accurate - its very likely that current had nothing to do with it.

To present a sound stage the mids and highs need to be reproduced properly. You usually don't need current for that since most speakers are fairly easy to drive in the mids and highs. Theils tend to have their weird impedance issues in the bass region, which has nothing to do with presenting a sound stage.

If the Onkyo has a power amp input I would run your preamp into that and see if you still say the same thing. Of course by now the issue might be moot since this is an anecdote; my point is that there were a lot more variables going on here than you initially surmised.

Our OTLs are known for a very good soundstage and yet they have a high output impedance so can't deliver the power into lower impedances. Our class D can- but the sound stage of our class D vs our OTLs is nearly identical.

Why do some amplifiers throw a bigger soundstage than others?

@rrm Two things: lack of phase shift and aural effects having to do with the 2nd and 3rd harmonics, the latter of which can make an amp seem more detailed and spacious.