It is difficult to be precise about your first error, since I suspect that the code you posted was not accurate, you will see why I think this in a moment. For future reference, if you post code then copy it from your editor and paste it here rather than typing in an approximation of it.
Still, what I think is happening is that you are calling your
Rec()
method something like:
newRecorder.Rec(newRecorder);
this is because the error message includes "no extension method 'Rec' accepting a first argument of type 'Julian.Audio.Utilities.Recorder' could be found", which means that you have called Rec() with an argument (the bit between the parentheses). You haven't declared a Rec() method with a parameter, so the system gets confused.
Two possible solutions
1. use Rec() rather than Rec(whatever)
2. in your recorder class, declare and write a Rec(Recorder recorder) method, but only do this if it is needed.
Please be aware that I will not be able to answer you for the next few hours. By all means ask further questions but do not expect a fast response.