"Cables?" is generally a much bigger question than a simple "yes" or "no" can answer. Short answer to the specific question: decent amping certainly helps, and tinkering with cable resistance changes the signature, but spending a mere 30 gbp for replacement cable won't ruin your sound quality.

Longer explanation: As a caveat, I am not a huge believer in cables after certain basic criteria are met. I switched my cable on the 595 out of convenience more than anything else. For my purposes (at that time) I wanted something shorter, and terminated in 3.5mm jack. I also lacked a soldering iron and space to tinker (at that time). The "custom" that I have is just mogami w2893 terminated to switchcraft 3.5mm. Mogami 2893, or comparable, is perfectly servicable cable for many/most headphone cable applications.

Back when I first swapped cables, I wanted to believe something was magical about the new one. More recently after experimenting with switching the stock cable and my "custom" cable back and forth, I find no noticable difference. Other people hear cables differently, and might notice an increase or decrease in quality. In my experience, the biggest limitation on the sound for the 595 is the driver. This is not true for all headphones.

If you are worried about keeping the same sound, buy the sennheiser branded replacement. But again, I would guess any replacement cable that isn't made of steel or using 32awg strands is going to be fine.