Hi! Just started encoding my cd collection over to my computer using LAME 3.90.2-ICL and settings "--alt-preset extreme".
Recently discovered that LAME 3.92 was released and now I'm wondering if I should start using that one instead. Any suggestions?

No, if you mean should you encode your collection again with 3.92.

Richi M - Wake Me Up CDS

Track 1 42.112.604 bytes 3:58
Track 2 104.268.908 bytes 9:51

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LAME 3.90.2-ICL "--alt-preset extreme"

Track 1 7.777.516 bytes 260kbps avg. (Winamp)
Track 2 18.385.545 bytes 248kbps avg. (Winamp)

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LAME 3.92 "--alt-preset extreme"

Track 1 7.555.337 bytes 253kbps avg. (Winamp)
Track 2 17.867.716 bytes 241kbps avg. (Winamp)

The reason for the difference in bitrates is due to either:

1. Different compilers being used between the two versions. Obviously, 3.90.2-ICL uses the Intel Compiler.

2. Different compiler switches are being used. Awhile ago Robert disabled some of the switches in the makefile which caused ICL compiles to produce slightly different bitrates than compiles made with other compilers.

In any case, there should be no real difference in quality.

any ideas on what the addition for Takehiro Tominaga's fix does with regards to quality? apparently you can enable it with --interch x. Can this be done with the --alt fast preset etc , Will it improve quality much?

Interchannel masking. If it works properly, you are able to get same quality at low bitrates. From what I've seen so far, it's probably not a good idea to use this unless you are encoding at low bitrates.