How to lower noise floor through mods?

Tubes that are tested for low noise might be the place to start. This would be a "plug and play" mod requiring only the effort to locate and purchase the tubes. But that romance and euphony might just be a product of noisy/micro phonic tubes. You won't know until you try.

Both caps and resistors will likely increase resolution and lower perceived noise floor. Retaining the tonal balance with these upgrades is a delicate balancing act. Most caps I've dealt with increase brightness to some degree, usually this can be adjusted for elsewhere in the system.

Modding power supplies may be helpful as well, particularly with the transients. I'm upgrading my Cayin's phono pre bridge rectifiers with HEXFRED's and bypassing the electrolytic caps with film caps next week, should have some answers soon. I'm looking for increased transient behavior, specifically more slam.

If you do go the modding route, just remember you can always undo the changes. I've also found modding to be the most interesting aspect of this hobby, really amazing sonic upgrades here! Endlessly replacing components is way too costly and relatively boring.

Mods are the way to go if you have some guts and soldering skills! Practice on cheaper pieces, gradually working your way up to more expensive components.

T bone, just looked at your system, like it! Also looks like you're comfortable with a fair amount of DIY.

The Jadis pre is nice, some VH Audio V-Caps, or better yet, some Duelund copper foil caps (depending on voltage ratings) should both give you what you're looking for. Others may have other cap suggestions, but the two caps mentioned above have to be on anyone's list of primo caps.

The Texas Components Vishay nude resistors (TX2575) are reportedly the best (I'll be making this upgrade soon to the Cayin). The Jadis is mostly point to point wiring which should makes cap and resistor upgrades easier.

Internal wiring would be my last upgrade, I like Mundorf Silver/Gold. Many others to choose from. NOS tubes and different isolation schemes may also prove very worthwhile.

Replace the rectifier(s)(whether a bridge or individual diodes) with soft recovery IXYS FREDs or CREE SiC Schottkys:(http://www.partsconnexion.com/catalog/semiconductors.html), and rewire internals with a good cable, like Kimber KCAG, going to a star ground with what would be the negative conductor and placing small ferrite beads on the positive conductors, at the source ends. Be certain your wiring is run tightly against the chassis, and(as much as possible) tucked in the bends along the outside of the chassis.

T_bone, if you have an older piece that you are wanting to update, the first thing to do is make sure that its actually working right first. To that end replacing the filter caps is the most important thing to do. You can get a lot of the aluminum can style caps from tubesandmore.com

Its not likely that improved resistors will be a whole lot quieter, but they will sound better. If you change coupling caps, which is where you will hear the most improvement, its a good idea to keep the following in mind: You can get better bass with larger caps, but you will pay a price in transparency and if the RC time constant associated with the cap is lower than that of the power supply low frequency pole, you will do your self a disservice. So I would stick with stock values for the most part.

Going to HEXFREDs is a nice touch although tube rectifiers are often lower noise. However, the higher output voltage that you get from semiconductors might allow you to install a high voltage regulation scheme. If you can do that, you will be instantly rewarded as long as the result is a B+ that is at least as high as stock! There used to be a device called the VB408 that was a high voltage regulator, very nicely suited for tube work. If you regulate, thats where you get the nice low noise floor.

Don't make a rat's nest of the insides. Keep your layout neat, with minimal wiring. It is a good idea to use a star-grounding technique and avoid using the chassis as ground. Its not OK even if the original manufacturer did it. That will help you get low noise too.

Have fun!!