Thanks for the description of your demo: I'm considering the Quad S-1 to use in combination with the Vena.
Your findings are surprising as the Quad S1s were reviewed well and not found to be typically Quad-like warm. Good to hear different experiences.
I've used the Quad Vena with Amphion Ion speakers. These (apparently) tend to be on the analytical side; I find them to be clear and detailed. With this combination the Vena has good bass, detail and soundstage in both classical and modern pop music. One caveat: I usually use the DAC of my Bluesound Node, although I also use the DAC of the Vena which indeed I find slightly warmer but only very slightly.
I'm not aware of the shortcomings you pointed out, but admittedly I've never heard the Rega Brio. Also you may have more experience in distinguishing aspects in the soundstage etc., I don't pretend to have 'audiophile' ears or extensive experience listening to different kit. Furthermore, I happen to listen precisely to the kind of music which you suggest might suit the Vena, while I don't regularly listen to the kind you've tried out. Still I'm wondering whether I'm overlooking something which other combinations might provide.
As regards the warm character, I've heard this more often and I can see what is meant there. The Amphions don't stress this so may be a suitable match, also they might provide more bass than the Quad S1s. On the other hand, I've read people recommending the combo with Harbeth P3ESR which are also said to be warm.