Harmonic Resolution Systems - under SS pre-amp

I have a couple of these isolation platforms - I have one under my transport and one under my SS amp. Yes, there was a sonic improvement when placed under the transport and to a smaller degree under the SS amp. My question is, and because they are not cheap ; ...would there be a sonic improvement if I keep continuing to add them to the rest of my system ? The next one would be going under a SS pre-amp ???
It's pretty hard to say if there will be an improvement. There will likely be a change, but whether the change is for the better is another matter. A lot of people think that any reduction in vibration (either from external sources or internally generated by the component itself) is going to be beneficial, but, that is not the case. This is an issue of tuning, which means "more" may take you beyond ideal and cause the system to sound too lean or analytical (I heard this clearly with some CD players).

You could do a rough experiment. You could put another platform under the cd transport or amp and use that HRS shelf to experiment with the linestage. You could first listen with the linestage not of the HRS platform and then on the platform. The HRS platforms I am familiar with are tuned to the specific weight and weight distribution of the component, so this would be a rough experiment. Also, since one component that formerly was on the shelf would not be on the shelf for this experiment, you would not get a full idea of the cumulative effect. Still, it would give you an idea of the kind of sound change to expect.

I would expect that the result would be far more subtle with the linestage than a source component, at least that has been my experience (using Symposium platforms/couplers).

Yes to your question.

Do you have the right weight on the HRS M3 and are you using the Spacers and Couplers?

If $$$ is not a factor buy as many as you can when they come up for sale on the 'Gon.

Do you have the HRS rack?
I would have put the M3 plate under the preamp prior to placing one under the power amp. The best a power amp or any component in a chain can do is feed the info given it by the prior component. Vibration is being introduced at the preamp, the power amp will communicate this. Try moving the M3 to the Preamp. I am willing to bet there will be significant sonic benifits. I certainly found this to be the case.
Interestingly, I tried the S1 under my components as an experiment and found it not to be as effective as the M3. I have used the nimbus and couplers and they are great as well but I found them to be no more effective than nordost pulsar point under the power amp. My guess is that the power amp will be the least sensitive, provided that it's solid state and not tube driven.
My 2cents experience : Have placed a HRS S1 under the TT and I believe the result is dramatic as it should be given the stylus/groove interface is the most susceptible to unwanted resonances. However, the most dramatic effect was to place 3 Nimbus couplers under the tube preamp. The result in terms of a tighter picture, less perceived noise noise and better all round definition was so impressive that I intend to add the Nimbus couplers to the dac and transport with maybe the small HRS iso plates on top off these components.
I suspect with SS components the effect may be miniscule, if at all.