my 2 cents:
everything about the Fyne F-702 screams that they go down to cover the bass frequencies (30Hz) and do it well. To add a sub to those without massive overlap is challenging. You either cut off the lows of a full range speaker with crossover control or you double the lows almost all the way, both are questionable approaches. I would get the least powerful 10" or 12" subs (2) and see if they improve anything. I spent a year trying different approaches until I successfully dialed them in. I ended up ditching the crossover and turning down the subs to 85Hz and very low gain. They just add a subtle accent to the lows, helping with the soundstage, but helping a lot.
@grislybutter There’s almost nothing I agree with here. “The least powerful sub?” Really??? If you position a good sub(s) properly and set the crossover, volume, and phase with any care whatsoever then good subs can blend seamlessly with most all speakers. That the speakers go down to 30Hz is totally irrelevant. 🙄 My speakers go down to 28Hz (-3dB) and I can easily integrate my “lowly” SVS SB2000 sub completely seamlessly. If you can’t do that then you really just don’t know what you’re doing IME.