Mert,
I'm using BetterCables... I had more expensive cables at one point (Nordost Frey) but I've never heard any differences between the expensive cables and much cheaper cables as long as both are built well and neither are malfunctioning. So I based my choice on the materials used more than a perceived sound difference, e.g. I chose copper with a thin silver coating so that I have that much more extra protection from possible oxidization of the copper layer than I would on just copper cables, since the cables run through the wall for distances as long as 80' (that wouldn't be fun to replace if there ends up being issues with the cables later on).
As far as amplifiers go, I'm very happy with the Ayre MX-Rs I'm currently using. With the W/P 8 sensitivity rating and these Ayre monoblocks, I really don't see any need to go higher in price ATM. I also like the Ayre design philosophy of handling the signal in fully balanced mode internally. My whole two channel setup is fully balanced from source to amp (except the turntable and phonostage). If I were to switch to tubes, I would switch to BAT gear in order to get that same balanced benefit from top to bottom most likely.
I suppose if you are in the market for an amp and don't care what it costs, you could check out the high-end Halcro dm88. I heard those Halcros with a dCS stack and B&W 800Ds... It sounded very very nice.