I had a lot of trouble with the Singnalink USB and the FT-891, but actually getting power out was not one of them. That said, I've been using FT8, Winlink and all other digital modes quite successfully with that hardware combination and the following radio settings (I did not need to adjust the Data Gain at all, since the Signalink has knobs on the front to adjust TX and RX gain!):
05-06: CAT RATE: 19200
05-08: CAT RTS: DISABLE
08-01: DATA MODE: OTHERS
08-02: PSK TONE: 1500
08-03: OTHER DISP: 1500
08-04: OTHER SHIFT: 1500
08-05: DATA LCUT FREQ: 100
08-06: LCUT SLOPE: 6db/Oct
08-07: DATA HCUT FREQ: 4000
08-08: DATA HCUT SLOPE: 6db/Oct
08-09: DATA IN SELECT: REAR
08-10: DATA PTT SELECT: DAKY
08-11: DATA OUT LEVEL: 50
08-12: DATA BFO: USB
Menu -> WDH -> 3000
The Signalink draws its power from the USB socket on the computer, so if your computer is not giving it enough juice, the powered hub may be necessary.
One thing to note, and it's hidden in the the Signalink USB documentation, is that the PTT mode in the software you're using should be set to "VOX". You do not set the radio to VOX, just the software. If you don't do this, the mic becomes active during transmit and other weird things happen (see this link for the full troubleshooting session: ). With the above settings, you will be using USB-Data mode. That's nice, because you don't have to keep switching between USB and LSB whenever you change modes/bands.
Good luck.
