I am also considering a similar 2 channel preamp amp upgrade.
The difficulty with any general question on feedback and advice relates to the prospective budget. I am a bit constrained on the equipment investment flexibility at the moment. While I have numerous thoughts on the amp side, a low(er) cost preamplifier seems to be a challenge. While it may not be an ideal solution for Croatia, the Schiit Freya S and Freya + are interesting here in the States. The Vincent Audio SA 32 or a lightly used SA 31 might be interesting in your parts.