Phono Stage upgrade to complement Dohmann Helix One Mk 2

@rauliruegas , if you listen to any modern music of course you do. It is all digitally recorded. I record other people's special records to my hard drive in 24/192. You can easily AB the recording with the original and nobody can tell the difference. In other words the full characteristics of my turntable playing a record are 100% maintained even after all this digital monkey business. It is also a lot of fun getting cool free music! 

@lewm , the problem is most commercial subs do not have any HPF. Yes, the LPF is always active. Analog crossovers add distortion and phase shifts. Some can shift phase 180 degrees with a knob but only by ear which is a trial and error nightmare. The crossover you are thinking about is too low. You should be up around 100 Hz to get the maximum benefit in terms of lowering distortion in the SLs. The problem is the subs have to be in time and phase with the SLs or you will hear them. this is true at 80 Hz also. I have listened to every crossover point and slope you can think of between 40 and 150 Hz 1 to 10th order slopes. As I have said before I can change crossovers on the fly from my listening chair. My Acoustats did better at 125 Hz. For some reason the SLs do better at 100 Hz. My guess is it is more surface area. Below that you start to loose headroom and increase distortion. Another issue is a subwoofer array for your system would be more involved than dr bond. He has 7 foot SLs with a high ceiling so below 200 Hz he is point source. You have 8 footers and if you have 8 or nine foot ceilings you are line source. In order to match the power projection of a line source speaker you have to have a line source sub array. This mean subwoofers at up to 6 foot intervals from wall to wall, corner to corner. I operate mine in stereo due to the high crossover point. Obviously, this is a more expensive set up but you are very clever and capable of building your own. 

@lewm , sorry I forgot to mention. At this moment I am using my outdated TacT 2.2X. I have a DEQX Pre 8 on order. It has a much faster processor so you do not have to worry about digital volume. When you lower volume in the digital domain you loose bits. With my Tact at low volumes you are worse than a CD about 12 bits. With the Pre 8 you are still above 24 bits. The Pre 8 also has four crossovers so I can see what a ribbon or horn tweeter will do above 12 kHz. There is the Pre 4 which is essentially the same unit as the 8 but with only one crossover for your subwoofers. You manage the units with your computer and a dedicated program. You can design any target curve equalizing the system any way you want. I keep mine dead flat until 100 hz where I increase the bass at about 3 dB.oct down to 20 Hz were I roll off steeply at 80 dB/oct creating a digital rumble filter. It also prevents launching your subwoofer cones across the room when you drop the tonearm:-)

If you look at the Stereophile review of even the old SoundLab A1, they measured the panel as flat out past 20kHz, so the need for a super tweeter escapes me. But of course ESLs do beam at HF. Depends where you sit, and your hearing acuity. Your present digital volume control would seem to be wanting in fidelity. Ok if you can run wide open.

@mijostyn  : " It is all digitally recorded.  "

For many years many of us knowed that and so what?. I can't control recording proccess. Can you?

R.

 Mijo, You wrote, "Analog crossovers add distortion and phase shifts. Some can shift phase 180 degrees with a knob but only by ear which is a trial and error nightmare."  Do you seriously believe that doing a DAC to ADC conversion, where also the signal is manipulated in the digital domain, in the signal path adds no distortion?  With the very steep filters you favor, there would be phase shift too; does your TACT enable you to correct for phase shift?  For me, phase shift is a non-issue, because with my speakers and no crossover, neither I nor anyone else can hear a 180 degree change of phase. Double-blind tested with my wife and son and other experienced listeners.  Once you add a subwoof, I suppose that phase between the main ESL and the subwoof needs to be set appropriately, but that is easy; there is just one variable.  I credit your taste in components (other than the digital ones), which makes me very curious to hear your system some day.  Maybe I'm just old-fashioned.