It's one in the same. How can you say losing him wasn't the problem in a hard cap league? If you don't lose him, you don't have to replace him.
Drafted Voynov in 2008, and it was a full 3 year development process before he did anything in the NHL. He was young, right handed, signed to a great deal, and it took just using a 2nd round pick to get him. Unless you luck out and get another Voynov in the draft(with or without the wait), anyone that you bring in that could replace him will either cost you cap space, and/or a current good player. What free agent is on Voynov's level that would cost the same cap hit? What team is waiting to trade a guy on his level to you, just to help you?
You would trade Muzzin for Trouba, but maybe Winnipeg doesn't want Muzzin. Maybe Trouba doesn't want to sign with the Kings.
http://www.espn.com/nhl/freeagents/_/year/2015/position/d
http://www.espn.com/nhl/freeagents/_/position/d
A trade might be the only real option, and we can see trades aren't as easy to make anymore with the cap. Without a cap, you could trade Brown's 11 goals and $6m contract to Toronto where he could be their 14th forward. With a cap, the best you can do is trade him for an equally bad contract, which there are few of. I think Girardi might be the only similar player/contract ratio.