Some quick tests:
No IS vs. Original:
foo_abx 1.3 report
foobar2000 v0.9 beta 13
2005/12/26 11:53:21
File A: D:\Neuer Ordner\aac_96kbps_cbr_no_is\Layla.mp4
File B: D:\Neuer Ordner\Layla.flac
11:53:21 : Test started.
11:53:33 : 01/01 50.0%
11:53:39 : 02/02 25.0%
11:54:44 : 03/03 12.5%
11:54:48 : 04/04 6.3%
11:54:57 : 05/05 3.111:55:00 : 06/06 1.6%
11:55:11 : 07/07 0.8%
11:55:19 : 08/08 0.4%
11:56:01 : Test finished.
----------
Total: 8/8 (0.4%)
IS vs. Original:
foo_abx 1.3 report
foobar2000 v0.9 beta 13
2005/12/26 11:59:29
File A: D:\Neuer Ordner\Layla.flac
File B: D:\Neuer Ordner\aac_96kbps_cbr_with_is\Layla.mp4
11:59:29 : Test started.
11:59:37 : 01/01 50.0%
11:59:44 : 02/02 25.0%
11:59:47 : 03/03 12.5%
11:59:51 : 04/04 6.3%
11:59:54 : 05/05 3.1%
12:00:03 : 06/06 1.6%
12:00:06 : 07/07 0.8%
12:00:09 : 08/08 0.4%
12:00:10 : Test finished.
----------
Total: 8/8 (0.4%)
IS2 vs. Original:
foo_abx 1.3 report
foobar2000 v0.9 beta 13
2005/12/26 12:00:42
File A: D:\Neuer Ordner\Layla.flac
File B: D:\Neuer Ordner\aac_96kbps_cbr_with_is2\Layla.mp4
12:00:42 : Test started.
12:00:51 : 01/01 50.0%
12:00:54 : 02/02 25.0%
12:00:57 : 03/03 12.5%
12:00:59 : 04/04 6.3%
12:01:01 : 05/05 3.1%
12:01:03 : 06/06 1.6%
12:01:04 : 07/07 0.8%
12:01:06 : 07/08 3.5%
12:01:12 : Test finished.
----------
Total: 7/8 (3.5%)
No IS vs. IS:
foo_abx 1.3 report
foobar2000 v0.9 beta 13
2005/12/26 12:02:00
File A: D:\Neuer Ordner\aac_96kbps_cbr_no_is\Layla.mp4
File B: D:\Neuer Ordner\aac_96kbps_cbr_with_is\Layla.mp4
12:02:00 : Test started.
12:02:14 : 01/01 50.0%
12:03:00 : 02/02 25.0%
12:03:18 : 03/03 12.5%
12:03:22 : 04/04 6.3%
12:03:33 : 05/05 3.1%
12:04:04 : 06/06 1.6%
12:04:10 : 07/07 0.8%
12:04:13 : 07/08 3.5%
12:04:15 : Test finished.
----------
Total: 7/8 (3.5%)
No IS vs. IS2:
foo_abx 1.3 report
foobar2000 v0.9 beta 13
2005/12/26 12:06:10
File A: D:\Neuer Ordner\aac_96kbps_cbr_no_is\Layla.mp4
File B: D:\Neuer Ordner\aac_96kbps_cbr_with_is2\Layla.mp4
12:06:10 : Test started.
12:06:31 : 01/01 50.0%
12:06:34 : 01/02 75.0%
12:06:38 : 02/03 50.0%
12:06:40 : 03/04 31.3%
12:06:54 : 03/05 50.0%
12:07:09 : 04/06 34.4%
12:07:13 : 04/07 50.0%
12:07:16 : 05/08 36.3%
12:07:18 : Test finished.
----------
Total: 5/8 (36.3%)
IS vs. IS2:
foo_abx 1.3 report
foobar2000 v0.9 beta 13
2005/12/26 12:07:47
File A: D:\Neuer Ordner\aac_96kbps_cbr_with_is\Layla.mp4
File B: D:\Neuer Ordner\aac_96kbps_cbr_with_is2\Layla.mp4
12:07:47 : Test started.
12:08:33 : 00/01 100.0%
12:08:36 : 00/02 100.0%
12:08:41 : 00/03 100.0%
12:08:44 : 01/04 93.8%
12:08:47 : 01/05 96.9%
12:08:51 : 02/06 89.1%
12:08:53 : 03/07 77.3%
12:08:56 : 04/08 63.7%
12:08:58 : Test finished.
----------
Total: 4/8 (63.7%)
Conclusion: all are more or less distinguishable from the original. When it comes to IS vs. no IS, no IS sounds better to my ears. For IS vs. IS2, no idea. I think IS2 was a bit better, but as you can see from the ABX logs, I didn't manage to get an acceptable result.
I also noticed that IS has an artifact during the first few seconds of applause. It produces something like a "Krr".