I love my Fyne 704 and am awaiting SuperTrax tweeters hopefully next week. I've had a few KEF products, and Technics Source Point C700k, however haven't heard the 888. I also have some JBL Horn compression tweeter speakers. I feel like Fyne are somewhere between a source point and horn, best of both worlds, with only a few minor downsides.
Great sensitivity and easy to drive, dynamic, with great imaging. They definitely come across as sound staging larger then the speakers size would have you believe, even more so than my JBL horns. However I don't believe that they image as precisely as a KEF source point design, so if I had to guess I would assume the 888 maybe give you a more focused sound stage. The one knock against the Fyne's is their sound characteristic doesn't scale as well as other speakers that I've heard, and isn't necessarily linear at all volumes. They kinda lose spatial depth and detail at high volumes (85db and above), which probably could be even lower for their smaller speakers. I do feel however they have a lot more transient detail, shimmer and airiness than what I had heard before from my KEF's. With only a Bowers and Wilkins diamond tweeter backed by 300 watts really catching my attention as the Fyne did when it comes to upper treble and high frequency reproduction.
I do really enjoy the speakers, and they can be driven with low watts, however I was surprised that mine being 96db the manufacturer still recommends 200 watts of power behind them. Presently I'm just using 30 Watts class A tube hybrid from my Levante.
What I can say about the Fyne speakers is that they are bar none the most enjoyable low volume listening speaker I've ever owned. If you are one of those kinds of people, which I am most of the time since I have young infant children. They almost seem to be better at lower volume at least as far as noticing that they sound amazing even when quiet, which I can't say for any other speaker that I've had. At least in the terms of how much I enjoyed them.
So if you have found horn speakers that you enjoy, and you so happen to like KEF like imaging. I would say the Fyne would appeal to you more. However if you dislike horn speakers, and want a speaker that can scale at louder volumes, then I would say stick with the 888. Again your ability to audition, and amplification obviously matters greatly. And again if you had a lower powered amplifier (≤100 watts) I believe the Fyne might work quite well for you.