I was just looking again at the Becos FX Yuna last night, never used it though, so I cannot speak to the Yuna, but I can go on forever about the Twain.
I have been using the Becos FX Twain Mk2 for a while and in "Stacked" mode (series) you get an optical-like sound. I go back and forth between the "Stacked" and "Dual-Band" Modes. I will say that the Lo SCF and Hi SCF knobs have cured my need for an eq pedal on my passive Stingray. The ability to boost/cut the Lo SCF (70Hz) and Hi SCF (3kHz) a bit has really, really helped me find the tone I need. You can also eq with the cross-over and the individual gain knobs. The other thing is the ability to control the knee/timing for lows and highs and the ability to select Feed-Foward, Feed-Foward/Feedback (lows/highs), or Feedback modes is amazing. In addition there is an preamp imput trimmer so you can boost/cut your imput. It can also serve as a buffer/boost with the mix set 100% dry.
The Becos Twain Mk 2 is really a lot of things in one box. After spending a lot of time just focusing on using the Twain solo I have found that I am using it as an preamp/eq and a compressor, which is really like having two compressors with the dual-band and stacked modes. Currently I like to run my Twain in Dual-Band, Cross-over at noon, Lows: Threshold 10 oclock, Ratio Noon,Feed-Forward/Hard/Fast with gain at 9:45, Highs: Threshold 10 oclock, Ratio Noon, Feedback/Soft/Slow highs with gain at 9:45, I keep the preamp imput trimmer at noon, and I boost the Lo SCF & Hi SCF a couple of dots = magic. Boosting the LoSCF/HiSCF was the missing link for me. Keep in mind you can tweak for hours if you let yourself, but you will find something useful, this thing is very flexible.
Note I am using my Twain as a preamp/eq/compressor. I am plugging my bass into the Twain Mk2 and into my Jule M700 power amp, simple and effective. I keep the tuner separate.
End of love note to BecosFX Twain Mk2.