If you change your preamp to something that isn't as warm and sweet sounding, you're going to end up having to change at least one other item mentioned in your list of components. I'm not saying which piece it is, but i see it as a sore spot in any system that strives towards neutrality.
Right now, the sonics of the preamp are probably balancing out / masking the sonic signature of this other component. As such, changing one without changing the other may be a step towards a LESS enjoyable and natural sounding system. Make sure that your money is right before you make a move on something like the preamp, because another expenditure will be right behind it.
Other than that, i agree with some of the comments mentioning the support structure that your gear resides on. A good support structure benefits ANY system but whether or not those results will be completely realized is up to the system itself.
If you like your existing rack, and there's no reason not to other than lack of adjustability / versatility, you might want to check into experimenting with various shelf materials. This can be done using different types of wood or other materials for not that much money and the results can be quite staggering / educational. If you want to get fancier with possibly better results, you might want to check into something along the lines of aftermarket shelving materials.
My suggestion would be to think along the lines of materials that have good rigidity, are non-ferrous in nature and offer low mass with high levels of internal self-damping. These suggestions apply both to the various woods / materials that you tinker around with on your own or with the pre-assembled shelving. This is a hard set of requirements to achieve for any one given material, so take that as a hint. Sean
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PS... Should you want to discuss any of this further, feel free to drop me an email. Just be patient with me as i'm way back-logged on getting through some of my responses.
