When I first received my Horizon, I put it through my Conrad Johnson ET7S2 pre-amp and yes, it did improve the SQ by a significant amount, but the CJ is SE and not XLR and luckily my amps will accept both.
Then I started tube rolling and that brought the Horizon alone to surpass the SQ level with the original tubes and the CJ pre.
Now I will try the Horizon with the new tubes AND the CJ pre to see where that takes me. I haven't tried this yet but will do in the next few days.
Fred