Preamp suggestions for Atma-Sphere Class D Monoblocks

A bit off-topic but I thought it important to mention that running a single REL sub with monoblocks and, separately, class D amps takes special care. I could not successfully configure a single REL sub with my BAT monoblocks. Had to use 2 subs. I was using the Speakon connector. 

So many great suggestions, thank you all! 

As @acman3, @armstrod and others have mentioned, the A-S MP-3 is a recurring theme, which is understandable, given the amp it will be paired with. It is definitely on my short list, as long as remote capability is available. Does anyone have comments on their ability to cast a holographic soundstage, realism and tonality?

Backert Labs gets a lot of love here on AudioGon forums as well. Interestingly, I met Bob Backert many years ago (at that time he lived about 25 minutes from where I am, in PA) when the seller of a Musical Fidelity preamp I bought on AudioGon recommended him to fix a problem with it. He impressed me as highly knowledgeable and as a modest, soft-spoken gentleman. I have no doubt that his products are outstanding. However, all except for the "base" Rhumba 1.4 are outside what I want to spend at the moment. Which, of course, may be all I need.

The LTA microzotl sounds great on paper, but probably not the best match for the A-S monos as it does not have balanced outputs. 

@osiris369, I am a fan of the BluOS platform as well and have owned many of their offerings - M10, C389(?) and was initially considering a comprehensive solution such as the M66 or the Bryston BR-20. I have decided ultimately to keep streaming and dac functions separate (as they change the most often) and focus on purchasing a pure analog preamp which is capable of sprinkling a little "magic" into the system.

@rmdmoore, thanks for the +1 for the Modwright LS100 - it is very appealing, especially at used prices. If I understand correctly, however, it is not a true balanced design so I don't know whether I will be losing something with the A-S monos?

As it stands, the A-S MP-3 and the Spatial Raven are tied at the top. It's great to have multiple options! Thanks again to everyone for your much valued opinions. 

I own a CarySLP 05 with ultimate upgrade. Bought it used a few years ago in pristine condition for $4300. It has a decent headphone amp. I’ve had great fun tube rolling and my current setup uses Raytheon VT231’s in the gain stages and CBS Hytron 5692’s in the buffer positions. I have a variety of VT231 and 5692 tubes to play with and it is fun to optimize certain characteristics (for example, Ken-Rad VT-231’s seem to have the most solid bass while still being creamy in the highs, while Sylvania seem to have a bit of sparkle in the highs, with this being heard from VT-231’s to NOS 6SN7 GTB’s from the 1960’s. 
 

Tube rolling doesn’t have to be expensive- I really like the NOS Sylvania GTB’s from the 1960’s that I bought at $35 matched each from Brent Jessee, enjoying them far more New Sensor Electroharmonix tubes.

 I have really enjoyed this preamp. Tremendous imaging with well-resolved holographic instrument placement, very quiet with black backgrounds, tremendous sense of dynamics and inner detail. Make sure to use a high quality rectifier tube!

It is definitely on my short list, as long as remote capability is available.

@srama The remote is an option (no charge); scroll down and you'll see it.

http://www.atma-sphere.com/en/mp-3.html

Decades ago when we developed the MP-1, part of that was figuring out how to do a balanced direct-coupled output which had to support the balanced line standard. We did that and have obtained two patents on the process. Before that, there were only two ways to support the standard; one is to use and output transformer and the other is a solid state circuit that can float and sink current at the same time (today there are semiconductor companies that make chips for this purpose). We patented a 3rd method.

In a traditional tube preamp, the biggest impediment to transparency and bandwidth (which includes the ability to cast a proper soundstage) is often the output coupling capacitor, which has to be large enough in value to allow the preamp to play bass when driving the lower input impedances of a solid state amp. That all goes away when you direct-couple and its the sort of thing that's immediately apparent.

@atmasphere, thank you for clarifying regarding the remote as well as the additional insight into the design.

I understand if you would rather not do so in a public forum, but it would be great to hear your engineer’s perspective on the Spatial Raven and the Backert Labs Rhumba, and how the MP3 differs from these designs (or provide some links if you have already discussed this).