So you have the data, stars look pin-point and sharp and to get it better you don't need hardware you need better processing and in the end more data in some cases. There seems to be some star distortion in the corners on some images so field correction would be the only hardware part to fix. Now you will be combining data from two scopes while you are behind on processing data from one scope - you aren't making it easy for yourself
There are topics where people share raw stacks or raw frames - try to process such raw stack and see if you are getting as good or better results as others posted - and if not ask how they got it and work on processing unless you get that end result. You already can capture data but you are far behind on processing when compared to the astrobin images you referred to.
Processing is the key definitely, that is not my top priority now, i will spend years for that for sure, in fact i tried not process anything to perfect, because that will make things much much worse for me, because when i get perfect results from ST80 i will go buy Esprit, another perfect results i will go buy Takahashi, another perfect results i will go buy PlaneWave, see, i will never stop then, i did that back in photography, i ended up with 5 full frame cameras and even i bought very expensive camera a digital medium format, no regret, didn't make me any better but i got fame in my community back then and i just moved on, if i was doing much perfect professional results with those cameras i might end up having 10 full frame cameras and 3 digital medium format cameras, you got my point.
I did process some of others RAW files, i got nice results, not like them exactly or better, but wasn't very bad, i wanted to play with my own data and spend hours with that, i will not feel happy if i made a perfect final result of someone free RAW data and then post it on here or Facebook showing people my processing skills, it was the data great quality, this is what an Indian guy is doing and he still doesn't have his astro imaging setup yet, now how much pain it will be if i used more scopes, only one way to find out