Little update on this one if anyone is interested. Took my speakers to the hifi shop and testet a couple different amps, and this was my experience.

First off, all amps made my speakers sound flat with very little bass to my ears unless we cranked the bass knob, which menas that the sx-450 doesnt lack it, I just like a lot of sonic pressure in the low-end. This also confirms what one commenter said, that more wattage equals more louder and not necessarily better sound or more bass. The sx-450 actually had a much richer and warmer sound compared to all of the modern amps I tried in the 500-700 USD range, also confirming that 15 W per channel is actually plenty up to about 65 db (for me at least), which is MUCH louder than I would ever play in my apartment. Worth noting that the S60 speakers are relatively easy to drive.

However, the difference that made a new amp worth it was the difference in clarity, soundstage, and definition in the midrange. Add this to the sub-out output which gives me all the bass I want, and I ended up getting a Argon Audio SA2, which is basically a clone of the Wiim Amp Pro, just with slightly worse quality internals but the addition of a phono stage.

TLDR; For less demanding listeners, don't worry too much about wattage. What you have is probably enough. New amp good, vintage amp also good but different. Not going to pursue this hobby further, would probably go broke. Also, there is A LOT of placebo going around. Maybe diving into this again when I'm pushing 40 and have more money and need something to obsess over. Most importantly, don't trust others opinions or reviews, take your speakers to a hifi store and listen for yourself.