[1] This one, for instance. Well, tubes doesn't make any sense... It looks like the distortion rating is pretty good - so it should sound identical to a solid state?
[2] And if it doesnt, it just sound plain worse, right?
[2a] This is essentially the one upgrade I would be looking to make in the future, but it probably doesn't make too much sense.
1. It should sound identical to an SS amp, provided the SS amp has the signal output characteristics required by your headphones.
2. There's no way to answer that question unless you define what you mean by "worse". "Worse" (or "better") is not an audio property, it's a personal value judgement that is not correlated to any audio property. For example, let's say that we're talking about fidelity and a particular SS amp provides a level of fidelity that is audibly perfect/transparent. If you then use a tube amp instead, and there is an actual audible difference, then by definition the tube amp cannot be perfect/transparent, it must diverge in some way from perfect/transparent (introduce some sort of distortion) and therefore be lower fidelity. However, the type of distortion that tubes often introduce is based on even harmonics and is commonly referred to as "Euphonic" (distortion). "Euphonic" means "pleasing to the ears". Effectively what we have (or can have) with a tube amp is therefore both lower fidelity AND more "pleasing to the ears", so then the question becomes: Is "lower fidelity + more pleasing to the ears" worse (or better) than "higher fidelity + less pleasing to the ears"? For me personally the answer is "worse" because I want to hear the recording made by the artists/engineers with as little distortion as possible and if the artists/engineers had wanted the recording to be listened to with this type of added euphonic distortion then they would have added it to the recording. For someone else though, "more pleasing to the ears" is by definition "better", regardless of issues of fidelity or artistic intentions. So, the exact same signal (output by the tube amp) that I can rationally/correctly categorise as "worse" can be rationally/corrected categorised as "better" by someone else and therefore, "better" or "worse" cannot be related/correlated with the audio signal output by the tube amp, it's not an audio property (it's purely a perception/preference), it cannot be objectively measured, there can be no objective/correct answer to your question and therefore your question is flawed/wrong!
2a. It would make sense if: A. You can easily afford it and B. The difference is audible and C. "More pleasing to the ears" is better to you personally than higher fidelity. If "C" is false, then it wouldn't make sense because you wouldn't be upgrading, you would be downgrading. If "B" is false then it also wouldn't make sense because you wouldn't be upgrading, you would be equi-grading, spending more money for exactly the same performance.
[1] If you look around you, you will see a huge number of products with names that include the words "pro" or "industrial grade". (Everything from sunglasses, to drain cleaner, to laundry detergent....)
[2] It's also worth mentioning that real pro gear doesn't necessarily perform well.
[2a] Often "being professional grade" has more to do with reliability, and how long a tool or item will last, rather than on its delivering the absolute best performance.
1. Agreed, but obviously, just because the term "pro" is routinely abused by marketing departments across numerous product types doesn't make it acceptable.
2. That's not strictly true, real pro gear does necessarily have to perform well, although it entirely depends on how you define "well". There are times when "well" can mean "terrible". An example I've given before is that of Auratone speakers, which at one time were found almost ubiquitously in commercial recording studios. They were terrible (they sounded truly horrific, which led to them affectionately being nicknamed "horro-tones") however, they were a useful professional tool because if you could get a mix to sound half-decent on horrotones then it would generally sound at least half-decent on anything. In other words, they "performed well" at being terrible! You don't find them in commercial studios much any more because the company redesigned and improved them!
2a. Certainly professionals require/demand reliability but usually with pro gear you can have reliability without compromising performance. In those few cases where you can't have both, sometimes we sacrifice some performance for reliability and sometimes the other way around, depending on the circumstances.
The obvious implication that marketing depends on is: As professionals depend on their equipment/tools for a living, which are covered as a business expense, then professionals tend to choose/use better (and typically more expensive) equipment/tools than anyone else. Therefore, "professional" means better and necessarily more expensive. In the audiophile world, the "abuse" is commonly three-fold! Firstly, their "professional" gear is not chosen/used by many (or any) professionals, Secondly, it's not chosen by professionals because it either doesn't perform better or actually performs worse than other pro gear and Thirdly, it's commonly even more expensive than top quality real professional gear! In other words, in the consumer/audiophile world, "professional" is typically just a marketing lie to justify a higher price.
G