Hi Libor,
I hope you have already downloaded sound files ( the songs you are learning from Kyle’s book)?\
Maybe this won’t be the best advice you could expect, but I would like to share my experience.
When I started learning those songs thos Bachido site didn’t exist yet, so had real hard time to learn just from the sheets ( I can easliy imagine your frustration).
But since Kyle uploaded sound files on Bachido, that made me learl the songs miles easier. Personally what I do is, putting those sound files onto your ipods ( or similar divice ) and listen just over and over again - well, whenever you can. Eventually it will stick to your mind - whether you want to remember or not it stays in your mind all the time! - downside of doing this is it still plays when you are in bed, it could disturb your sleep really bad 
Whether you realise or not, if you take formal lessons in Japan lots of teachers won’t give you tab until you memorise the whole song - or sometimes you never get a tab! Not because all the pro shamisen players are mean, but learning from sheets is not practical for tsugaru shamisen ( I guess lots of tsugaru shamisen performance is improvisation basis, so there is no need to write down anything.)
For Bachido members like us, we have only limited resources, so sheets can be the big part of reliable resource, but STILL I believe that sheets should’t be the first resource. By listening again and again over time (even subconsciously) eventually you will be confident to play with the help from sheets, because the notes on the sheets are nothing new, they are already in your head.
Hope this will be a little bit of help.
Good luck and enjoy your sound files 
Sayuri