you can use
VirtualTerminal.DataReceived event to log the text yourself. Use the
DataReceivedEventArgs.StrippedData property to get plain text.
Telnet client = new Telnet("server");
VirtualTerminal vt = client.StartVirtualTerminal();
vt.DataReceived += new DataReceivedEventHandler(vt_DataReceived);
void vt_DataReceived(object sender, DataReceivedEventArgs e)
TerminalControl.DataReceived event works the same way.