sorry for the late reply, I just got home from work.
Depending on what speakers you go with you would probably want more power then the sa-50 can provide. Also it’s more a quality power concern as well, I would recommend something not class d as ime class a/ab sound better and offers higher quality power for your speakers. I would start looking in the $200 and above range, some good stuff to start out with would be a Emotiva basx a100 or a Parasound Zamp v3. My preference is the Parasound. A little higher up would be a Parasound new classic 275v.2 which would be pretty nice.
So even front ported speakers still get some benefit from being pulled of of the wall, just to a lesser extent. I run KEF Q100 that are front ported on one of my desks and they do enjoy a little space. I’d say at least 9-12 inches.
It’s good for what it is and would be a bit better than the SA-50 I think, but ultimately still a Class D measurement based design. Which some people like but it would be more similar in performance to what you have already than not. I think if you really want something higher quality you would want to look at some class a/ab amps like the ones i mentioned above.
I have the RB42s on one of my desks and they are a fun little speaker that has some decent low end in nearfield. Just something that i like to run on my workbench with a cheap smsl bluetooth amp and not worry about SQ. If you are looking for something more impressive than what you already have I would look higher.