...your Cambridge Audio Topaz? You can look at its specs for headphone output and it will tell you the recommended range of headphone impedance.

According to Crutchfield, the Focal Clear Mg is rated at 55 ohms, so as long as that's within the range of the amp, you're good.

That's most likely the impedance for speakers - NOT headphone output.

Which model Topaz do you have?

Some homework for you:
https://soundslack.com/headphone-impedance-explained

Since I have not personally auditioned the SR10, Jotunheim, nor Clear MG, I won't make any recommendations for/against any one of those. (No doubt, other members will be more than happy to share their opinions -- and then some.)

Your proposed pairing of the Focal Clear Mg and an amp like the Jotunheim could be interesting via a balanced connection -- however, even if you had provided all headphone output specs of the SR10, I would still say that only you would be able to define "great improvement" by actually listening and comparing.

On the objective side of the coin, a quick search reveals that the Jotunheim is found on Audio Science Review.

manunkind wrote:

Thank you very much!

I reckon I'll get Focal Clear, plug it into my SR10, and if I feel I'm not getting the fabled sound of magic I will start hunting for the dedicated amp.

Sounds good - you can always add equipment.

Would encourage you to inquire about return policies before selecting your vendor.

My personal fave is Crutchfield, and they do carry the Focals you want. They're pretty good about answering any questions you may have about the products they sell, so it doesn't hurt to call 'em.

Post back when you get your goods!

RE: Topping
My observation is that they submit a number of its products for review by ASR since the number of sites that posts reviews seems to be limited.

For sanity's sake, it's best to approach internet reviews simply as documented opinions -- nothing more. (And that they are to be taken with a grain of salt.)

As you may have noticed, ASR posts measurements of the products it reviews -- much unlike the former editor of the now defunct Audiostream who used to describe anything/everything he liked as "warm" since he "didn't have the resources to do measurements." (How TF does something sound "warm" anyway?!?!) Such measurements compiled by others should be utilized as baseline and comparative data -- not as a single source of truth.

ASR posts its financial support methods on its site -- however, if someone has gained better insight by auditing their review process and/or bank accounts, sure would help if s/he would chime in and enlighten us all. And if there is such a thing as an Authoritative Data Source on measurements and objective reviews, then s/he should share that, too.

John Atkinson does an excellent job with his reviews and measurements on here. One such example - which may be of interest to you - is the not one, but *TWO* reviews he did on the Asus Xonar Essence ST/STX. (This is the second of two: https://www.stereophile.com/content/asus-xonar-essence-ststx-soundcards-follow-september-2010)

Had it not been for his insight, I might not had even known about the card, let alone end up buying two of them a few years ago.

Given JA's review states "Headphone output level & impedance: optimized for headphones with impedances of 32–600 ohms", why not use the Xonar (at least for now)??

I realize it may not be first choice, but at least give it a try and see how it compares to the Topaz.

...either the Clarks or Audeze.

These are what I have:
https://www.stereophile.com/content/terrific-hifiman-he400s-planar-magnetic-headphones

(Also have a pair of Grado, which are of course, also open-back.)

InnerFidelity is no longer, but you might be able to search and find some of their reviews elsewhere online. Would also search on "InnerFidelity Wall of Fame".