Where to use Isolation devices

I think I use them in the following order:

Turntables
Tube Equipment
Analog Sources (i.e. CD player)
pre-amp
amp

I have three Nordost Sort Kones under my SACD player and actually think that they made a real difference, but doing a quick A/B comparison is impossible so it's difficult the be sure.

Turntables, so I'm told, are very sensitive to vibration as are tube based equipment. I think I remember reading somewhere that Nordost recommended starting with the analog sources and working from that end.

My personal opinion is that I wouldn't bother using isolation for digial sources, but some will tell you differently.

There are several different types of isolation devices. Some decouple the equipment and others couple it like the Sort Kones. I think different ones can work better or worse for different pieces of equipment.

I know the guys at my local hi fi store went mad when they got the Sort Kones. The finally sent me home with a set to try out with the promise of a free return. They have almost every piece of equipment on them to the point that they had to steal from equipment to find three for me to take home.

I liked the effect of BDR cones under my SS preamp, but I found them even more
effective when used with Herbie's Grounding Bases.

Under the power amps, I use Herbie's Iso Cups. These are tube monoblock units,
so I would guess you stood to gain too if you used Iso Cups under your own
amplifier.

I tried myrtle blocks under my CDP and they helped, but Herbie helped even
more. Tenderfoot footers this time. Another thing that will help your CDP is
electrical isolation: a small isolation transformer. Also, a reasonably-priced
aftermarket power cord is worthwhile on a CDP. I use an Acoustic Zen El Niño.

I use Herbie;s Tenderfeet under everything I have except my Burson integrated. It has a thick and heavy case (6mm) that not only serves as the heat sink but is so effective at isolation that it makes the Tenderfeet a moot point, otherwise, I'd use them there as well.

I use Herbie's products under everything. The items used, placement and number vary by the piece of equipment.

I have tried uncusccesfully to "mix 'n match" manufacturers when it comes to isolation devices. In my opinion, I find it better to ID a manufacturer you like through some auditioning and then build your isolation approach with that manufacturer. Most I have spoken with, including Steve at Herbie's are very helpful.

For example, my TT rests on a Gingko isolation device that itself sits on a slightly larger 4" thik solid maple platform due to size issues: the foot print of my TT is larger than the top shelf of my Billy Bags equipment rack. Herbie was very helpful in working with me on products he does not even sell.

My two cents...

I use devices under everything and believe everything seems to benefit, including speakers. I use a range and don't believe myself, you need to use the same throughout.
Herbies products are always good value, I use the Isocups. I also have some Stillpoints and Black Ravioli, a UK product. Both are excellent and better than the Isocups, but a lot more expensive, even second hand. I have used or tried some brands I did'nt like, particularly HRS. In my system, they did'nt have much impact.
I am sure the way to go is to look out for second hand products on the Gon or other sites and just try them out.