"have you tried/tasted their steak?" if you've been talking about the restaurant, so the listener would understand whose steak you're talking about.
alternatively: "have you tried restaurant name's steak?" or "have you tried the steak at restaurant name" works. You could optionally add "yourself" to the end of either sentence, which doesn't really change the meaning but reinforces the question of whether they have firsthand experience (slightly more interrogative).
In the same vein, the use of "ever" has a sound of incredulity to it, like you think they're talking about something they haven't actually experienced. If you started off the conversation with "have you ever tried matsuzaka-gyu," it wouldn't have this connotation, but if you had been talking about a particular wagyu restaurant and you asked "have you ever been there/have you ever tried their beef?" It would sound like you expected the answer was "no."