Aurender ACS10

Thanks for adding your virtual system. Very helpful. Nice system. I have to agree with @lalitk. The N2x series was a notable improvement over the previous generations... but there is a real possibility that you would not get the, "Wow, that sounds A LOT Better"... that should come with an upgrade. But you might. 

I think your system would benefit from a N20. This would be a step up. Somewhere in here an upgrade of you preamp would be appropriate to bring it up to the level of your speakers should be considered. If it were me, I would do the preamp first (I am a big Conrad Johnson fan), then the streamer. 

OK ghd. At 90 years old soon I have no right to make mistakes for what will be my last improvement. So which preamplifier could replace my CJ? ARC, CJ, Manley, Cary, Cayin, new or rather used.

@andreleon36 

 I’d start by upgrading the DAC before anything else. My suggestion would be a DAC from Lampizator, LTA, or the AQUA (like La Scala Mk II).  Any of these would represent a substantial step up from the Mytek both in musicality and overall refinement.

https://www.audiogon.com/listings/lisbf056-linear-tube-audio-aero-dac-new-da-converters

https://www.lineartubeaudio.com/products/aero-dac-digital-analog-converter

There are many used DAC listings here and on USAM. 

https://www.usaudiomart.com/details/650256201-aqua-la-scala-mk2/

Maybe and CJ ET7SE? This is a contemporary CJ Preamp. Changing brands would add an additional level of complexity. I think the CJ is a very complimentary preamp in your system.

Lampizator, LTA, Aqua ,are not available over here in France. 

CJ ET7SE used not found . What about a used Cary SLP98P ? or aARC LS27 ?