I have to say that I am really impressed with Horizon and delighted to have it together with the Extreme which I am also very impressed by. The two together are the end of the road for me.
My main DAC is/was the T+A SDV 3100 HV which is a digital technological tour de force and a great digital hub. It is very similar to Horizon in that it has an analogue preamp stage with a single RCA and XLR balanced analogue input and it has been very interesting comparing them and figuring out how to use them both in my system. Initially, I ran the Horizon into the analogue input of the SDV where it clearly sounded best at max 63 on the volume. I preferred this since it seemed a little airier and more refined than Horizon direct to power amp. Over time, I came to realise that I preferred Horizon direct to the power amp. This may have been my ears adjusting to the different presentation or certain changes that I made or perhaps both. The Graphite cones and cups opened things up and made it a little more airy and refined, so too did introducing the Tak 274B giving the aspects that I preferred whilst utilising a preamp together with the greater clarity, energy and transparency of going direct to power amp.
Then I ran with both SDV and Horizon plugged into my power amp and just switched between them to compare - I did also try a separate preamp but preferred Horizon operating as the preamp. I also concluded that I preferred Horizon as a DAC/Pre to SDV as a DAC/Pre.
At this stage, I was wondering whether I really needed the SDV but, appreciating how good the digital section is, I then tried running it into the Horizon as a preamp and it sounded very good. So, currently, I run Extreme to Horizon via USB and to SDV via Ethernet Roon Ready mode and both sound great giving me two different options. I also run my CD transport into the SDV DAC utilising the more analogue type profile and on into the Horizon. This too sounds very nice and has given CD a shot in the arm. Whether this is just temporary or not, I don‘t know. I suspect that it may be but it’s nice to have anyway.
My conclusion so far is that, in my setup, the Horizon is a really good preamp. My final discovery phase is to determine whether I prefer Horizon as DAC/Pre or the SDV DAC into Horizon as Pre. Currently, I am really liking both and they are different enough to contemplate keeping both in the system.