Im looking for the next upgrade. I'm not real sure which way I want to go Help!

I am looking for a fuller sound I’ve heard ESL 13’s with a Gryphon Mephistopheles and was very impressed. Right now in thinking what I have is on the anemic side

I don’t think using the streamer as a preamp is doing you any favors at all, and I’d look to try a good tube preamp that I bet will yield improvements across the board. What’s your budget? I’d highly recommend looking at this Don Sachs pre that will add life and tonal richness to your system yet still with excellent, natural detail, and it’s only $2450. If it doesn’t work just turn around and sell it for little/no loss, but many say this is an end-game preamp. Definitely worth a shot for what you’re looking for IMHO and could save you big $$$ over other options.  My bet is it’ll blow you away just going by what you’re hearing now and how elated other Sachs pre owners have been.  Just my $0.02 FWIW.

https://www.usaudiomart.com/details/649919944-don-sachs-model-2-line-stage-preamp/

The MLs will sing with good tube pre and amp combo.  Adding a sub can be fun if it's set up well, but I'd definitely make letting the MLs breath the higher priority.

I use a pair of ML Impressions with an ARC tubed preamp and a Classe two channel amp. It has delighted me for years, and I have never felt a sense of fatigue and or any kind of thin sound. 

I would recommend a Audio Research tube preamp. This would be the next step in refinement and fidelity. I would recommend buying used and look in the $5K range.

Enthusiasm for this pursuit is key and admirable. The increases in fidelity are nearly limitless. I have been pursuing this for over fifty years and each upgrade during that time has rendered my system’s sound better and much more enjoyable. But to get the very best sound requires a great deal of planning and research.
 

You have done really well so far. I think after purchasing a great preamp I would spend a lot of time listening and learning before embarking on the next steps. As you move on you will want a well thought out game plan for future upgrades. I recommend Robert Harley’s The Complete Guide to High End Audio as a great place to get the lay of the land.