I tunes appears to have no problem ripping the same CDs to apple lossless, using the same optical drives, rip speed is upto 6x, so I assume the disc is actually OK
That is, unfortunately, not a valid assumption.
MC uses Secure Mode to rip discs. This means that it verifies that the data being received is identical to the data originally encoded on the disc (via CRC error checking and other mechanisms). If MC detects unrecoverable errors, it slows down the ripping process and tries to get it right. This means that, by default, MC ensures that the rip is 100% bit-for-bit identical to the data that was originally written to the disc.
This mode can be disabled, but that is not recommended, unless the source cannot be replaced and there is no other option.
iTunes does none of this. It does not care, at
all, if the content it extracts from the disc is full of skips, blips, and garbled data. It can tell if the drive itself is reporting errors (and will then, also, slow the ripping speed down to compensate), but if the drive just can't properly read the disc, or the source data is damaged, iTunes will happily encode the damaged audio.
So... The behavior you described is not unexpected at all with a damaged source disc.
Another application that has similar Secure Ripping features, if you want to do an apples-to-apples comparison, is
EAC.
As far as the potential causes? There are a few possibilities:
1. Damaged disc. This is the most common cause, of course.
2. Faulty data cable connecting the optical drive to the computer. This is probably the second most common cause. This is especially true of the old parallel style ribbon cables, though SATA cables fail (or get loose) fairly often as well.
3. A faulty (or misbehaving) SATA port on your motherboard. If those optical drives are connected to an "alternate" SATA port on your motherboard, as opposed to the ones "supplied by" the Intel CPU, these are
often finicky about optical drives. For example, there is a common Marvell chip used to support extra SATA ports on many motherboards that doesn't work properly with any ATAPI device (all optical drives, tape drives, etc) at all. Make sure, assuming those disc drives are internal, that they're not connected to a non-standard SATA port inside your computer.
4. Damaged disc drive. This is less likely, but still possible. It is also possible (though exceedingly remote, unless the drive is a very old one) that it doesn't support some of the ATAPI functions required for Secure Ripping.
5. A much less likely, but still possible, culprit is software issues. These could include bad or missing drivers (the motherboard's storage drivers are the ones relevant), malware, DRM crapware (Sony's old rootkit junk), etc.
In any case, the fact that iTunes "succeeds" tells us nothing about compatibility, or the quality of the disc. I could probably run a disc over with my car and iTunes would "succeed" in ripping it.