Argyle won the fourth round 1-0 thanks to Ryan Hardie's penalty in the second-half.
Muslic said afterwards: "It was a magical day for us. Playing in the most famous cup in the world, against Liverpool, it is big already. To win this game is something that will remain forever a part of this club and history and the lads deserve it."
On the club's new signings settling in quickly: "It was never about signing players as soon as possible, it was about signing the right players. We have managed to do that, that was the plan. In the end we deserved to reach the next round.
"We are very much looking forward to the next challenge. Hopefully it can be another home match. The next game is the most important and on Wednesday (against Millwall in the Championship) we have to go again.
"I'm so happy with this penalty (Ryan Hardie) scored today and I will keep this forever in my heart. We have created momentum over the past three weeks and we have to move on.
"This is the biggest moment in my career so far. Hopefully, by the summer, I will have another big moment in my career when we stay up."