Hello, BAKTRA in newest release add TURBO D, so now u can try convert games to this Slovak Turbo format, which allows 4000-9600 baud speed, i have good experienece with 7000 baud, more is problematic for me, but one my friend have lucky with 9600 baud (wav file from turgen).
This turbo is interesting, if error, loading stops, u can turn little cassette in backward and try again read that block. sorry for my english :/

loading basic file, device D:, 2 blocks

loading atari tennis, device N, 1 block, 6000 baud

schematics and all documentation (SK language) is here:
http://atari.turiecfoto.sk/