All versions of LZX are bugged.
How do you know this?
For audio, Shorten (.SHN) will always beat FLAC hands-down. Approximately the same compression but shorten uses massively less CPU power to decompress.
And has far fewer features than modern lossless codecs. I also doubt Shorten is as good as modern codecs. And last but not least, I use a fast peecee for playback, and FLAC uses up an infinitesimal amount of CPU time here. On Amigas I use WAV. Much faster.
Anyway, seeing how the OP wants the best compression rates and it's for archiving, FLAC would be the way to go if their data was mostly audio.
2. You forgot to assign T: to your hard drive somewhere. I know its dumb and not your fault but that is just how it is with lha making large archives.
Why would anyone want to assign T: to their HD?
Until you can prove LZX is bugged, I'm gonna stick to LZX :p