It is my understanding that this client application is no longer supported and will not be receiving further updates. Your only choices are (1) use the web client, or (2) build a client yourself using the 3CX Call Control API.
What you are talking about, essentially, is building a wallboard plus the ability to manipulate users and calls through the same interface. This is perhaps the most complicated type of application we have ever had to build, so it's not fun. It is almost straightforward to handle basic calls, but when you start having people create conference calls, and listen / barge into calls, then keeping all the events straight becomes pretty convoluted. This would require a significant effort.
Unfortunately, for all but the deepest pockets, your only option is the web client.