As a manufacturer we keep saying that we are done that is until we hear something that sounds better to our ears. For example, we were using Audio Note capacitors in our components until we removed them and added chokes to replace them. Big change maybe but noticeable and an improvement plus they are cheaper than the AN capacitors.
Your weakest link is not having a preamp but by saying that it depends on the flavor of the sound you are looking for and it cannot be just any old preamp either.
Glad you are happy. You don't need anyone to tell you any different.