Hi m8!
Since I am the proud owner of one I will try to shed as much light as possible on your concerns

For reference I play mostly classis rock. My setup is as follows:
1. Atma
2. Les Paul
3. Zilla 2x12 with 1 Greenback and 1 GH12-30
4. A pedal or two (allthough I must admit It dont really need any pedals)
dgaemc2":jvlfkmj5 said:
Anyway, my questions are as follows:
1. I require a great clean sound (I use an HSS super strat type guitar). Does the ATMA offer great clean sounds in Ch1? Bogner markets Ch1 as offering "blackface and tweed sounds" which I realize are just reference points. However, my primary concern with this amp is that in Ch1 the "tone knob" might really be more of a "gain knob" which transforms it from "blackface type sounds" to "tweed type sounds" without having the ability to shape the clean sound (no tone knobs) in Ch1. The only tone shaping for Ch1 seems to be the treble toggle for low, medium or high. Does anybody find this to be a limitation in Ch1?
I can understand your concerns on the clean channel, however on my Atma I have not been able to break up the clean/crisp sound without cranking the volume and tone at max, and then it barely breaks up. And this is with the Les Paul Burstbucker pups. Don´t forget you have the 3 position bright switch to shape your tone as well. Saying that, I have seen the videos where they seem to play the clean channel and getting it almost crunchy, but I have not mannaged that. It really feels as if the tone knob is more a treb/mid boost then gain. The only limitation I feel with the clean channel at this point (with the lack of a proper EQ), is when you put a OD-pedal in front of it. I have not yet found an OD pedal that works well with the clean channel, but I have only tested two so far.
2. Does the "vintage / modern" toggle switch in the back of the amp apply to all 3 channels or just the high gain channels (2 and 3).
Since it is in the power amp circuit I belive it shapes the entire amp, but I can verify this later tonight.
3. I tend to hear a lot of noise from this amp on the youtube clips that I have listened to (even when the guitar player was using a humbucker pickup)? Is this amp inherently noisy?
My amp has almost no noise at all. Sure there are some when you really crank it, but that is just normal. And I hate noisy amps! Listen to Giovannis video (linked later), no noise at all in that one.
4. My "normal" settings for this amp would probably be setting it for a nice clean sound in Ch1 (using the single coil pickup options of my HSS) and either the 60 or 70 setting for Ch2 & 3. Most often probably the 70 setting based on what I am hearing on youtube demos. Secondly, I would be playing it through my 112 Avatar cab with a V30 speaker which has the option of open back or closed back. Is this amp capable of providing me with great sounds based on how I would normally use it, or is it more suited for a harder rock aggressive sound?
It´s impossible to say, but I really love this amp, and I belive it can dial in pretty much anything you want, except ENGL hyper gain. It´s definetly not a one trick pony i.e "Hard Rock Aggressive". Running CH2/3 in 60´s mode with cranked gain and a strat/single coil will give you an awsome Hendrix like crunch tone. Switching to 70´s and you get some more classic Zep-gain, and 80´s just shape things up getting it a bit more modern, but not recitifier modern rather something in between. The 112 CAB will probaby work great. I think this demo is one of the most accurate:
https://www.youtube.com/watch?v=FgPavwAness and Giovanni plays on a 112 Two Rock in this one. Allso give you a hint on the cleans.
5. Assuming that I would be able to achieve very nice clean sounds in Ch1, does it have sufficient headroom to reasonably hang with Ch2 or Ch3 in a rehearsal / gig situation?
It´s a loud 18w for sure. I can not really comment on this, but give me to after tomorrow and I try it out with the band.
6. I know that some of my questions are very subjective, but I just want to get a better understanding of actual ATMA owner opinions regarding this amp prior to ordering one since I have no option to trying one out in person.
I know the feeling, and I am happy to try and shed some light for you.
7. This amp really appeals to me because it offers 3 footswitchable channels in a very small and light weight package. I do own a Mesa Mini Rec which I do really like, but find clean headroom on that amp a bit of an issue. Secondly, I really like the fact that the ATMA is a 3 channel footswitchable amp head in a very small package.
Thats why I bought it. 3 Channels with one dedicated as clean. Allthough now I would have wanted it to be at least a 5-6 channel amp

It´s so versatile and as I said you can dial it to almost anything you want, thats why I would have loved one or two more channels. Guess I will have to buy another one and A/B them

Having said all this, when it comes to the power it is LOUD! Playing with the band in a rather small rehersal room I have never set the volume passed 12' o clock, and that is on 80´s and modern setting. Last rehersal I ran it with the Vintage setting and the volume never went pass 11, and we have a rather loud drummer (dont we all)
If it lacks anything I would say that a "real" EQ on the clean would have been nice, but thats because I would have liked an OD on that channel to get it even more versatile then it is. Putting a good OD-pedal there and I might be able to get that sweet just cranked blues sound as well. This I plan on fixing by finding the right pedal (an OD-pedal with an EQ).
Well I guess thats pretty much it.
/ Richard