Sony CRX175 doesn't burn above 4x

I have a new CDR Sony CDRX175e 24X burner.
Some cds burn at 16x, some at 12x and others at 8x and 4x.
I tried Nero (with latest CDROM.CFG), CloneCD and NTI CD-Maker 6. Same result.
I'm not interested in burn at 24x but I need to force 16x.
Is that possible?
 
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