A nice tube in the pre section which a nice alternative to the RCA 6SN7/VT231 is the Sylvania 6SN7GTA.
By the way, I reluctantly recently sold my Cayin A88T for an Almarro 318B. The Cayin is much more dynamic and powerful, however, I purchsed some Zu Druid speakers which mated nicely with an Almarro 318B, which has the trademark SET palpable mids, although as mentioned, it gives up something in bass control, dynamics, and soundstage.
I tried several SET amps, and the Almarro 318A or 318B to me is one of the best. It wasn't an easy decision because the Cayin A88T has something the Almarro doesn't and vice versa. With the Zu Druids, the Almarro roars and its 18 Watts per channel is plenty.
As a side note, I personally like the older Zu Druids better than the new Zu Omen speakers. They both sound similar, but to me, the Zu Druids are slightly warmer in the mids and still have very good bass down to the sub frequencies where it falls a little short (a good blending musical sub is the 100 watt MJ acoustics or an REL), and the newer Omen, although similar, is slightly clearer sounding overall and has more slam and a little more bass and a tad more treble it seems.