Esoteric K-03 or K-01

Denon1,
It sounds very much like you are having a great time with the K-01.
And you are also happy driving your power amps directly. Your amps and speakers clearly are all singing together in synergy with the K-01.
I am curious as to what filter settings you have settled into.

Jon2020, as for today my K-01 has about 300 hours on it and all that time I use 4 upslamping and SDLY1 filter. To me this combo sounds most dynamic and airy. But next step I will try is to burn 2x with FIR1 filter becuae this combo has a potential to sound great also.

Hi Denon1, after break-in of Slow Delay 1 and 2, I found 4X with SLow Delay 2 to be more harmonically interesting and open sounding than Slow Delay 1. Slow Delay 1 seemed instead more tube-like, and a little limited in bandwidth. G. with Slow Delay 2 to have

JON202, I think the Vienna music arequite efficient speakers and that the reason (yours and partially mine) that you have to set volume control almost to the max on your K-01 because Bryston has low input impendence and K-01 does not have enough juice to drive Bryston direct. My krell has much higher input impendence, but still I feel that I have to compensate with much higher volume setting to get better dynamics, bass and soundstage.
And you know that both Bryston and Krell are great with dynamics and bass.
So I think I have to agree with Guido advice and we have to get active pre-amp to get full potential from our gear. It will come with the price so.

Denon1,
You are correct about the Bryston"s impedance. Also, my listening room is rather large and the VA Die Musik speakers are not super sensitive, ca. 87 dB, while their impedance can drop rather low at times. So, they need to be cranked up for optimal sonics. But, since I am not losing much resolution(bits) at these digital volume levels, I might be happy to just carry on without a pre-amp for a while.