Hi Remy,
Is your goal to modify the sound of your system to one which you prefer or to see what difference altering the digital cable can make?
If the first, I suggest you have a wide range of alternative free options. The on-board DSP capabilities of your processor and speakers provide a range of programmable options which could support the changes you wish to make: Tilt could strengthen the bass and soften the treble, Axis in my systems affects intelligibility of voices, etc., etc. All such changes are quickly and easily compared and reversible. You might even revert to the standard processor software to see if that is an improvement...

Your room position and treatments are also ways of experimentation but there is a thread elsewhere on that subject.
I suggest that stock Meridian cables are probably well-engineered and meet the SPDIF standards. If you try alternatives, they may introduce euphonic improvements by varying from that standard. I recently replaced the 8m long standard M- and S- leads in my smaller system with some Atlantic 1m SPDIF cables, purely to tidy things up. I
think the sound is better in terms of bass extension, treble sweetness, separation and dynamics but would not swear to it and I have done no back-to-back testing. Was this perceived change caused by the change of cables - who knows? BUT, I not only changed the make of cable, I also changed the lengths, the routing and, of course, cleaned the processor and speaker connections just by the act of unplugging and plugging the cables. All these variables may be candidates for any change in sound - if indeed it exists.
Good luck with your experiments and please let us know what you find.