All of them really need changing is the answer, but if only one then the source to pre first.
As after my experience of what a 552dr does to the sound, i think the better the quality you can keep from the source to the pre will result in a better overall result. As the pre is going to change the sound anyway
Having heard various cables, I am a big fan of Morganas. Testing them meant lots of back and forth, which reinforced the conventional wisdom on 2 points: the standard cables are pretty good, and near-source cables matter more than those further down the signal path.
The weight of advice here is source to preamp connection before worrying about the pre-amp to power amp. I would agree. Whichever you choose, I would advise looking at the used market. You’ll find plenty of offers in all the usual places.
We’re not concerned by our speaker cost as a percentage of system. Our 5 Powerlines, at current RRP, would cost more than our speakers. They were all of course sourced used.
In our room the Sonetto are most enjoyable. I always thought they were perhaps slightly light in the bass, but the 300DR changed that and they’re now wonderfully balanced across the piece. They work well with a wide range of musical styles.
We may choose to move on long term. Our local dealer carries SF so home audition of Olympicas would be possible, but the III would be a 12k investment.
At the moment we’re focused on maximising output from the current hardware, in the same way we did when we had 272/250.
I will be honest, this is the desired order. However, I had 1 & 3 in place first. I was waiting for an SL (Din to XLR) to come on eBay at a decent used price. When I finally replaced the OOTB Naim supplied cables between the pre-amp and power-amp, it was a massive difference. Much clearer and deeper bass / cohesion. I do find it slightly odd that Naim provide such very cheap cables when you buy a 40,000 pre + power amp combo. The OEM cost of those cables is peanuts…