UPDATE: OK, I have some feedback after flashing the kernel and tweaking CPU/DSP frequency (echo 0 > /sys/power/op_dsp). Unfortunately, drop-outs are still there - no change in that matter.

I've noticed something even stranger - when I start playback (using Canola and/or Kagu - tested both), I usually can first hear a split-second sound, then nothing (although song is still playing in the player), and after 5-8 seconds I can hear the music back again and then it plays normally without major drops. Same thing happens at the beginning of almost every single music file (and time varies, sometimes it's like 1-3 secs, sometimes is 6-8), so let's say I have album with 10 songs, and I have few-seconds drop out at the beginning of each one... It seems to me like player is buffering (?) a song at the beginning, which takes some CPU time, hence drop-out for A2DP...