I too run the Icom IC-718 and have NO problems here.
My Station is of course the IC-718, Tigertronics Signalink USB Sound Card Interface, 230foot Delta Loop Ant.
There are NO Menu settings for running Digital on the IC-718.
Since we both use the 13pin ACC Port here are the setting I use. (No USB-D or USB-L or any of that)
1. Radio's RF Output from the Menu set at 100watts. (Signalink USB TX controls the RF Output)
2. Radio's Mic Gain level from the Menu set at zero.
(Remember to reset it for Voice ops. Also Mic is NOT disconnected when TXing from the ACC Port so Mic Gain has to be zero to avoid picking up any Back ground noise and ALC will show as none.
3. Comp and DSP functions all turned off.
(Also note to Ken KB3MDT I strongly discourage use of the Mic Jack where the ACC Jack is for this purpose)
With the above settings, my Signalink USB controls the RF Output and the Receive Gain via the TX and RX Level controls on the interface and I can run the TX Power up to 100watts or as little as possible.
4. What Sound Card program are you running, FLdigi, HRD/DM780, MultiPSK or MixW?
Anyway questions drop me an Email.
73 de Steve KB6HOH