I agree that a SignaLink is not *needed*, but it sure is a quick and easy way to get FT8 and other digital modes working. Most people use isolation transformers between the sound card and the radio. If you simply wire a sound card to the radio audio input and output you run the risk of introducing hum and noise from grounding issues. The SignaLink has those transformers built in to provide the isolation. I've been building digital interfaces since the early days of PSK31 (before the waterfall) so I understand that it is possible to make a good interface yourself. I even had one published in QST. However, I have also used a SignaLink-USB with several radios, including my IC-756PRO. It's all a matter of how much effort, you want to put into it. Whatever you do, make sure that your Tx signal is clean with no hum or noise.