Can better parts.....

Can better parts really translate into better sound quality? Thinking of having my Arcam FMJ23T modded by a respected modder, to include master clock, resistors, op amp, power supply, RCA connectors, etc and possibly the addition of a tube stage. Can I really expect an improvement in sound quality?
Yes it does. A better clock will help greatly. Better output caps would help,greatly. I have improved the sound of many, many pieces with better parts never experiencing anything but improvement.
Better parts can sometimes translate into better sound. And sometimes not. But simply arranging for better parts to be installed does not make for a better mod or a better modder. The modder needs to be intimately familiar with each particular circuit or piece he's trying to mod - otherwise it's kind of a crapshoot at best (and possibly an expensive one). An expensive modder is not necessarily a respected modder. So take all that slowly. But, I do agree with Grannyring's post.
They can most certainly in the hands of a skilled craftsman that understands the overall design case by case, but no guarantee in general. The devil is all in the details.

I would expect a difference in sound with the specific combo the OP relates, most likely for the better, but only if done well by someone who really knows what they are doing.

Parts are just parts. Its what is done with them that always matters.

I would recommend that for whatever cost might be involved for any particular custom mod, especially pricey ones, options to replace or upgrade to different well received high value gear be considered as well. Sometimes better results can be achieved more easily replacing rather than tweaking. All surgeries usually come with some amount of risk.
The use of better parts like Duelund CAST caps are a no-brainer and always make gear sound better. No need to know the circuit, just replace that cheap cap with Duelund CAST or top line Jensen copper foil.

The improvement will shock you folks. No risk here with some known to be top end parts like Duelund caps and top end connectors.

I have done this in speakers, amps, CD players etc... and each and every time the result was a wonderful revelation. Builders often times use parts for cost reasons only. It's reality and reasonable.

Replace that Alps pot with a nice stepped attenuator and prepare to hear what your preamp can really sound like. Replace that $12 output or coupling cap with Duelund CAST and your once ok preamp is now darn good!

No need to mess with changing the circuit, just know the parts that are critical and upgrade to the best. If you like the piece of gear you have, but want to hear more of it, then this is a fun and reasonable way to go.

You must like to tinker and solder and enjoy it as part of the hobby. Your labor is free and the results can be astounding for the $ spent.

Go ahead and look into your $15,000 piece of gear and learn what parts are used. I have been floored and amazed at some of the cheap and simply ok parts used in these very, very expensive pieces of gear. After all the mark ups builders simply don't have the freedom to use the best parts.

The gear having these best parts are priced accordingly.

Understand this is not for all and if you are constantly selling, then beware as the value after your mod may drop. I have found it sometimes increases the value however if your work is good and the part brand well received.
If you know what you are doing, and correctly replace specific parts with other "Higher quality" equivalent parts electronically (like a capacitor of equivalent specification), I would expect only positive results. That's always how good things might become even better.

The question will always be how much and is the investment a good one.

That's not always a question that is easily answered, but if one can answer it with confidence, and not put things at risk otherwise, for example by voiding a manufacturer's warranty in the process, have at it.

When one party modifies another's device, that always leads to questions regarding whose problem it is if something goes wrong. ie who ends up paying to get things fixed.

Then there is always the resale value aspect of things as mentioned. Modified devices can be hard to categorize and resale value can be nebulous and even negatively affected accordingly compared to more "known quantity" type items.

Personally, I shy away from buying most anything that has been modified by a third party used, especially if pricey. I prefer to invest in more known quantities that have been positively received by many. In other words, the maker got it right for my purposes right out of the box.

I'm not saying don't do it, rather just be aware of what one might be getting into before pulling the trigger, especially with a third party mod as opposed to doing it yourself and knowing what you are doing.
You can generally get improvements upgrading series signal coupling caps, like VCaps or Dueland. Other caps like powr decoupling may be hit and miss or have little effect unless you know what you are doing. Having modded lots of components over the last 13 years, I have reverse-engineered many of them. Sometimes this is what it takes to get significant improvements. Another thing you can do is replace the bass inductor in the speaker crossover with a good air-core ribbon inductor like the Jensen.

Modders that can rverse-engineer a component and do the right mods with good rework quality are scarce. Pne good thing about usingma modder is they have done the footwork of identifyingmthe best part to use in a given situation.

Steve N.
Empirical Audio
Yes better/different parts will change the sound. But parts swapping is not the only answer. Adding a filter choke to lower ac noise or making changes that use a more direct route can have offer better sonic improvements versus just part swapping. Simply resistor changes can make improvement at a much reduced cost. Experimenting with part swapping can get expensive especially the higher priced capacitors. You may get different sound but how much better will it be for the price? All caps have a sound and none of the ones that I have tried are perfect, I seem to always give up something.

Happy Listening.