6 Moons has a super review on the A88, so I'm not sure if your comment on "brittle and hard" is justified.
I mean my Jadis OR KT90 does have its weakness, but overall its a superb image.
No tube amp in the under 2K range will be 'all things".
I've only heard good things on the A88, not one poor report. I will say tubes do make a huge difference. I bought a quad of EH 88's for my Jadis just to test as a comparison to the 90's, and did not care for the 88 at all. I also bought a 88 amp to test and same results, very flat.
Audio Research uses 88's and i do not care for ARC amp sound.
However Cayin makes a graet product as my Cayin 15 and 17's testify.
Bottom line, seek out some good KT88's and also play with the pre tubes. You have much more potential in this amp with the right tube.
I do not like the "british" sounding tubes, Mullards etc. I love RCA's NOS. Of course it can be expensive to roll tubes. Try to buy from a seller you trust and will take them back if you find that are not for you. Maybe a 25% re-stock fee may be part of the offer.
I have a local tech guy who helped me find incredible pre amp tubes for the Jadis and also for the Cayin 17.
Enjoy the amp in the meantime