Will an Amp change improve my system ?

The S300 is a fine amp for the price, but for me the Pass was much better sounding...don't know your speakers though...some love Benchmark, but very many do not...

First of all how big is your room?…after you answer I will give you my honest opinion if you can handle the truth…let me know …

I had the PRIMALUNA EVO 400 preamp and amp…not impressed 

To answer your question, no, an amp will not significantly improve (or hurt) a system regardless of what the sufferers of expectation bias will tell you.

your list includes warm tube amps and analytic dry amps, complete opposites, do you know which sound you like?

Changing your power amplifier can improve your system, but as the saying goes, “it all depends.”  I changed from a highly-rated tube amp to Odyssey Kismet solid state monobloc amps that are twice as powerful as the stereo tube amp.  The change was dramatic and instantly noticeable.  It depends, however, on your preferences and the specific characteristics of the power amplifier involved.  My earlier change from a highly-rated solid state amplifier to the tub amplifier did not sound as well, hence the switch back to a solid state power amp with my Rogue Audio tube preamplifier.  
 

Let your ears be the judge, but there is very good counsel be had in this forum.