Yeah, you don't need more than 4 channels for what you are doing. However, if you want to run your single-ended headphones in an active ground configuration, you would still need the 6-channels. It's up to you though: some say that the 3-channel configuration for single-ended usage brings it closer to true-balanced.

ah, okay, active ground. Isn't this the way the Corda Opera runs?

No, a 4-channel won't give a 3-channel single-ended amp. It will be the 2-channel without the active ground. IIRC, most of the reviews of the Beta are based on the 3-channel single-ended version. So the minimum would be 5 for an active-ground single-ended and the option for balanced.

edit: For more reading, check here.

So let me get a little clarification. Lets say I wanted a balanced beta22. Lets say I have some balanced headphones, but I still want to be able to listen to headphones with regular 1/4in jacks. All I really need is a 4 channel, right? The only point of a 6 channel is so that two people can listen at the same time with unbalanced phones?

You're close, but let me try to clean it up the last little bit.

With a 4-channel configuration you can listen both balanced and unbalanced. Four channels is all you need for balanced operation but the single-ended side of things with 4 channels would be using what is referred to as a "passive ground".

With a 6-channel configuration balanced operation is identical to the 4-channel setup however in single-ended operation both SE outputs would be driven with an "active ground". Folks like tangent, amb and others have long argued the benefits of an active ground channel. I won't pretend to understand it all or even be able to accurately explain it but if you want more information I'll try to dig it up for you.

Why would it not be possible to use a relay, and flip a switch:

Ground the input to one of the negative boards, and send that out along with the L&R of the positive boards. One board sits unused, but you stillg et active ground out of a 4 channel setup.

Personally I never did hear the benefits of an active-ground configuration, having heard both the Corda Opera and the M3.

After all, why go pseudo-balanced when you can go full-balanced? If you are at this level of performance, might as well go all the way.

Then I guess the next question is how much more expensive is a 6-channel then a 4-channel?

I have not built one, my guess is around the order of $250 - $300 but nate would have a much better idea.

Then I guess the next question is how much more expensive is a 6-channel then a 4-channel?

JB's pretty much nailed the parts cost for the additional two boards but the biggest expense is in the chassis. The least expensive option that I'm looking at for the two chassis for my beta22 is ~$400 (total). I've seen folks cram a 4-channel build into a single chassis (not recommended in my book) which would halve that number. Also, by going to 6 channels you'd need to use 2 power supplies, a 4-channel build could run off 1. There's another $100 there.

Personally I never did hear the benefits of an active-ground configuration, having heard both the Corda Opera and the M3.

After all, why go pseudo-balanced when you can go full-balanced? If you are at this level of performance, might as well go all the way.

F___'in Aye!!

Well, for me the excuse used to be that since I didn't have a balanced source (and wasn't really planning to have one) that I might as well build the best performing single-ended rig that I could. Of course that's been rendered moot now with the new DAC but if I was an SE guy I'd still go 3 channel instead of 2, the cost difference isn't that great.

As I have stated before, in reference to the M^3, I am not yet a believer in active ground design. I fully intend to test this out when I finish my amp. When talking of the M^3, the three channels are already on board, but for something like the Beta, It would still cost roughly $100ish bucks to add an extra channel, and at this point, I don't think that is worth it. We shall see if I believe it in a few weeks, as I do some opamp rolling into the ground channel (as well as bypassing it).

in all the amps i've heard, balanced sounded more transparent than single-ended. the 3-channel active ground does lower output impedance, but does nothing for slew rate. full balanced is the way to go.