I've learned just enough about Irish to get in trouble. I want to use the name "Faigh Amac", Sound Out in English, for the chat app (https://rocket.chat) I'm connecting to a forum I'm building.
https://www.focloir.ie/en/dictionary/ei/Sound+Out
It would be a kindness if someone could confirm this is the correct form of the expression, before I make a fool of myself.

Thanks in advance

You need to be more specific. Whether you mean "sound out" in the sense of "thanks a lot" or "that person is sound out (reliable)" or "sound out the alarm", each would require a different translation.

Normally when you give someone a dictionary lookup, it is the first meaning unless specified otherwise.
In this case I can only presume you confuse Shout Out with Sound Out. There is no venacular for the use of Sound Out in the context I "did" give, a forum .

As if that wasn't enough the first and second dictionary entries made it more specific. The question, as I repeat, is not what the words mean, but whether it's use would be illogical to an Irish speaking person in this context, a chat within a long-form forum . To clarify what I mean by chat, this is similar to Slack and includes Video Conferencing,
Rocket Chat https://rocket.chat

To wit: sound out = faigh amach
1 (v + adv) ascertain opinions; try for information TRANSITIVE
to sound sb out about sth a fháil amach cad a cheapann duine faoi rud, tuairim duine a fháil faoi rud, barúil duine a fháil faoi rud
let's sound out the staff on this issue faighimis tuairimí na foirne ar an gceist seo, téimis i gcomhairle leis an bhfoireann ar an gceist seo

2 (v + adv) ask about nature, substance of; try for information TRANSITIVE
faigh amach

You sound annoyed at my response. Theres no need to be. It's better that I clarify what you mean by your request and give you a correct answer than that I assume you're happy with the first dictionary entry you show us and tell you that's fine, not knowing in what way you intend the phrase.

Faigh Amach means something like "seek out". From what I understand, you want to name yourself something along the lines of this, but in Irish. If this is the case, I'd say go ahead and use faigh amach. Of course, it's important to wait for input from others on here to ensure you're getting an accurate translation.

By the way, I have not confused "shout out", a distinctly American phrase, with "sound out", a phrase with a particular use case in Ireland. I don't know of anybody in Ireland who uses "sound out" as an expression meaning to "ascertain opinions; try for information". If somebody said it to me I would assume they meant it as a way of saying "thank you". If somebody had the name "sound out" on a forum, I think most Irish people would take it to mean the person were declaring themselves to be a pleasant and/or reliable person. Context matters, and a link to an online dictionary page is not context.

That's very interesting, Ade. Of the three uses of "sound out" which you indicated as likely in Ireland, I've never heard the first one used here in the US, and the other two would be said here without the word "out", as in "he's a sound person" or "sound the alarm".

The expression "to sound someone out about something" is very common here, though. Muir, if that's what you meant, then all three of the examples you found in the dictionary will work, although the last two mean more specifically "to get someone's opinion about something":

a fháil amach cad a cheapann duine faoi rud [as a sentence fragment, since something would need to come before the "a fháil"]
tuairim duine a fháil faoi rud
barúil duine a fháil faoi rud

As a slogan or heading, then, Faigh Amach would seem to work well.

_________________
I'm not a native (or entirely fluent) speaker, so be sure to wait for confirmations/corrections, especially for tattoos.

Just to clarify your square bracket comment:

Grammatically, all three are verbal noun phrases ("infinitive phrases") and can be used so where appropriate.
So nothing more would need to come before a fháil ... cad ... in case of the first expression than anything need to come before tuairim a fháil or barúil a fháil.
It must not be a sentence fragment but could be a headline or so.

The "a" in a fháil amach cad ... is not the same as in tuairim a fháil , i.e. it is not a verbal noun particle (do > a, "to") (which need to have a subject or object before it).
It is a possessive adjective ("its") referring to cad ... ("its finding out what ...")

What's funny to me is, until this thread I just took it for granted that "sound out" was a fairly common expression of thanks in the English speaking world. I suppose it must be an Irish-ism. I'd never heard it used in the context OP was seeking, or as you mention, "to sound someone out about something".

As regards the other two candidates I suggested, you'd probably be more likely to hear "he's sound out" than "he's sound" or "he's a sound lad", but both variations are certainly common in Ireland. "Sound out the alarm" sounds very archaic to me, and you'd be much more likely to hear "sound the alarm", but I think you'd sooner hear "sound out" in this context in Ireland than in the context OP was looking for.

https://www.teanglann.ie/en/eid/faigh_amach

Yes friend CaoimhínSF, my presumption was a use of "to get someone's opinion about something". In the times and places I was raised in Sandys Parish, Bermuda were claiming to be displaced Southern Irish (the Bermuda Island) was a common family joke, Westover AFB (9th Bombardment Wing, Sep 4, 1956 – Mar 31, 1974) at Chicopee, Massachusetts, and Madisonville, Ohio (just outside Cincinnati), and in those communities from 1950s through 1970s the phrase to "Sound Out" someone was as common, as to say a person had "Sound Judgement" or had a "Sound Reason" for doing something.