try more dictsize (d2048) or (d4096) in lzma (try it)
in the last version of srep 3.93 acept more than 1gb of dict
in arc.ini add -d1g or -d4g (you choose)
Code:
[External compressor:srep]
header = 0
packcmd = srep {options} -a1 -m3f -d4g $$arcdatafile$$.tmp $$arcpackedfile$$.tmp
unpackcmd = srep -d - - $$arcpackedfile$$.tmp $$arcdatafile$$.tmp