cables are they worth it?

Don't think of designer cables as "

better teh a $50 wallmart cable.

Rather, think of it as wire that's better adapted to the requirements of sound reproduction... IOW, here, more expensive is only better selectively.

Anyway, JPS is an interesting wire. However, at the cost, I would hesitate (unless funds are plentiful) and probably opt for solid-core cable instead, for interconnects. There are plenty of alternatives; one cheap alternative is DNM.

Let's not go to Walmart for cables. It is against our religion as audiophools. Home Depot for DIY is respectable even Rat Shack would be better.
That said your amp isn't in the same class as the rest of your gear. The amp is the heart of a system , it is the engine of your system, save your money get that amp first, you can buy used Signal Cable for now it is very inexpensive and good enough.
I bet You will see that a good integrated or monoblocks with a pre are much better, and don't be scared off by tubes. Obviuosly mono blocks and the peamps in particular are expensive but man they can be incredible, I found Nirvana with Opera Consonance Cyber 800s which are tubed monoblocks 75-80 wpc and a used AES-3 pre also tube but only two. The AES-3 cost me 350 or less used what a steal I wish I could find a phono stage as good. Either an integrated or a better power amp will take you a big step forward heading to Nirvana.
BTW I like Cardas too but once it is in the chain you get the effect downstream so don't worry about that.

Borrow some from other locals and experiment. You aren't the only audio nut in the Netherlands. Cheers,
Spencer

Both cost around $800 each for 1 meter

Others will disagree, but $800 is much better spent elsewhere, IMHO. There is absolutely nothing wrong with ordinary Walmart cable in most cases. How much is better construction, better shield, better looking and better connectors worth to you? Fundamentally, wire is wire - and there is nothing toxic about Walmart wire - except perhaps lead paint on the connector??

If it makes you feel more secure in the knowledge that you have a couple of impressively priced, high quality and rare interconnects then go for it. (For some, eliminating the agony of doubt/fears about their system sound quality is worth this price)