Where to invest the most in the "digital chain"?

Dear All,

I'd love to get everyone's opinions on where best to invest/invest the most, in the "digital chain".

Using my current "basic" system as an example I have very good Internet service into a very good router with the stock PSU on a dedicated power conditioner strip with an ifi AC iPurifier. From there I have Audioquest Pearl Cat6 to a Cisco 2960G with an upgraded Russ Andrews Power Cable. There follows another AQ Pearl Cat6 to an English Electronics 8Switch with an ifi iPowerX. From there I have the Chord C-Stream Ethernet to my ifi Zen Stream with a 15V ifi iPowerX. Then a Wireworld Chroma 8 cable to an ifi iPurifier3 into a Zen DAC v2 also with ifi iPowerX. The EE8, Stream and DAC benefit from a power-conditioner/surge protector and a pair of AC iPurifiers.

I've got a SotM iSO-CAT7 on order which I am intending to put between the EE 8Switch and the network transport with a dCBL-CAT7u into the network transport.

Phew, that was a lot of words!

My question is, and this applies to all systems as a generic question, where is it best to invest the most? Should the best Ethernet cables and/or switches and/or isolators be first in the chain (i.e. from the Internet source) or at the end of the chain (into the DAC/Music Streamer/Network Transport)? Similarly, where should the best power supplies be placed? Or does it all matter equally?

This is purely about the digital chain, I'm well aware that great speakers and a great AMP with good power and speaker cables make all the difference too!

I'm interested in opinions and I will of course experiment for myself.