My Xiegu G90 radio has to have the output from the 8-pin connector in the back set to line instead of mic for it to transmit a digital signal into my SignalLink sound card. Could it be that the FT-450D has the same type of settings. which may need to be changed back again from line to mic to send SSB or voice.
With correct settings for the transceiver's CAT interface in the Winlink software, Winlink should be able to control the transceiver. There should be no need for another "computer control program" interfacing with Winlink.