Hi, and sorry for my english.
I've waited to try the Knoppix release 5.3.1 before to decide to write this POST!!!
It seems that a very strange bug/issue is present into all the 5.x.x releases: if the boot optical drive is a SCSI device (but I presume this is valid for almost EVERY NOT IDE boot devices), during the initialization I receive the following error message: "can't find knoppix filesystem, sorry".
This happens even choosing the no hardware detection and/or the expert option. Sequentially, I can see: the searching for USB/Firewire devices, the DMA activation (if enabled) for the IDE devices and, finally, the HDD and Optical Devices enumeration. Quickly after this last operation, the aforesaid error message appears.
This happens ONLY when I select a SCSI optical device to load Knoppix: my PC1 starts Knoppix 5.x.x without any trouble when I boot Knoppix from an IDE device. I must to say moreover that both the test's machines run Knoppix 4.x.x without issues (but this old release don't recognise the SATA ICH9 and/or the Jmicron IDE CTRLs).
I can suppose that The Knoppix kernel makes, after the mass storage's detection, some kind of device re-enumeration and this operation changes arbitrarly the optical device logical position. After this, Knoppix becomes unable to find again the CD/DVD source.

Below, the test's machines:

PC1 - P4 3.0GHz on Intel D865PERL MB
1.5Gb ram DDR 400
ATI Radeon 9800 AGP
Intel IDE CTRL ICH6 (OnBoard)
IDE DVD-RW Samsung
IDE DVD-RW LG
IDE Maxtor 320Gb P-ATA
Adaptec SCSI CTRL 29160
SCSI HDD 35Gb IBM Deskstar
SCSI CD-RW Yamaha
SCSI CD-Rom Toshiba
Qtec IDE Raid CTRL 320R
IDE HDD Maxtor 20Gb (Backup Unit)
LAN 1Gbit Chipset DP83820


PC2 - Core 2 Duo E6300 on Asus P5K
2Gb ram DDR2 800+
ATI Radeon HD2600 XT PCI-e
Jmicron IDE CTRL (OnBoard)
IDE Maxtor 320Gb P-ATA
IDE Maxtor 120Gb P-ATA
Adaptec SCSI CTRL 29160
SCSI HDD 35Gb IBM Deskstar
SCSI DVD-Rom Pioneer
SCSI CD-RW Plextor
SCSI CD-Rom Plextor
LAN 1Gbit Chipset Attansic L1 (OnBoard)