Hi there
I was first introduced to Entreq grounding about 4/5 years ago by their UK distributor and I now have an extensive suite of their products and I also use their i/cs,power and speaker cables.
My profile lists the main ones.
I have found them to be very effective. They just banish the veils that are there without them and the resultant sound is so much purer and unsullied.
IMHO the best starting point is a grounding box and associated Eartha cables. Most if not all Entreq dealers will allow you to try them in your system so you can decide whether they benefit your system. There is obviously the issue of budget and the good thing is you can start in a modest way and expeand as funds become available. It is also importnat to keep a balance between spending on Entreq and other system upgrades be it amplifier, speakers, whatever.
You could start with as little as a Minimus ground box and one or two earth cables, or a larger Tellus and more Eartha cables. My first experience was a Minimus and modest earth cable connected my then CD player and the improvement was immdeiately audible.
Entreq products are readily available used and the boxes and earth cables are invariably safe buys, but the usual rules of due diligence apply.
I hope that gives you a helpful introduction and happy to answer any more detailed questions.