How to find the good CD recordings?

Since you will be playing CDs, or any form of digital music, you need to learn about "The Loudness Wars."
https://en.m.wikipedia.org/wiki/Loudness_war

There’s also another period in CD history; for a short time when CDs were being introduced, some masters were not transferred at the proper specs for a digital disk, so they suffered from poor quality. Many were recalled or thrown away, so it’s unlikely to find one.

Your Arcam may be a fine player, but the rest of chain is also important for revealing good SQ from music recordings.

Start buying some used CDs or "sale" items and see how they sound. If you have a decent system you’ll be able to hear the disks that suffer from overcompression. They have limited dynamics, most noticable in the bass. It’s not deep or tight and the bassline usually blends into the rest of the instruments. There may be a wide soundstage, but there won’t be much of a 3D image.

I just took a quick cruise through some of the Hoffman threads on Zep and there appear to be three major eras: the ’originals’, which I gather were mastered by Barry Diament; the ’90s era George Marino remasters and the John Davis remasters that were done at the time the Zep catalog was reissued on vinyl in the last several years. There does not appear to be a consensus (shocking).
When those new vinyl issues came out, I bought the first three albums on LP, just out of curiosity, and though they were clean, quiet, had deep bass and were very ’clear’ sounding, they didn’t convey the same immediacy and punch of some of the better vinyl pressings, e.g., the US RL mastering of II, which may be the best sounding Zep record extant. It has a freight train delivery.
None of the Zep albums are in my view of audiophile quality-- it is somewhat sad, given the significance of the band, that they weren’t able to put together better quality recordings.
That said, I bought the recent vinyl reissue of How the West Was Won, which was also mastered by John Davis, and it sounds surprisingly good for a live recording.
I’m sure there are outliers out there too-- for example, my best sounding copy of LZ1 on LP (and I have quite a few different pressings, some rare or expensive) is a Japanese pressing done in the early ’70s on Warner-Pioneer. That’s the reason why I suggested you take a listen for yourself. I am a fan of the early Zep (my favorite album is still the debut which is a poor recording in my view) and spent a fair amount of time and money buying multiple copies (mostly older pressings) to find the ones I thought sounded best. That said, it was a somewhat expensive, time consuming endeavor. I suspect you could do the same with the CDs, and it probably wouldn’t cost as much, but it would be time consuming. And, even with that, different ’pressings’ or masterings are often strong in one area and lacking in another. So, you wind up picking the versions that best match your listening preference and system strengths/weaknesses.
Now you’re gonna get me to start evaluating these things on CD!
PS: I just took a quick look on Discogs and the Diament mastering of LZ 1 seems to cost about 3 bucks! (Granted, most are a little more expensive, but if that is reflective of the cost of most of the CDs, you could do these evaluations yourself pretty cheaply, at least compared to sussing out the vinyl LPs). Good luck, and have fun, part of the enjoyment of this is the hunt. 

lowrider, interesting that you mention the loudness wars. I don't think loudness and volume are the same thing but certain CDs are definitely louder at a given volume than others. A new CD I purchased recently by a new glam band, The Struts, is noticeably louder than most of my other CDs. The quality seems fine, but they're not really a sit and listen type band. (Going to see them in October. They're nothing earth shaking but they are a breath of fresh air in an otherwise pretty stagnant rock landscape.

lowrider, my system is an AR LS16 tubed pre-amp and a Madrigal Proceed HPA2 (Levinson) amp with Aerial Acoustics 7b speakers. Totally inherited, I had nothing to do with their selection. Not sure how it stacks up but is leaps and bounds better than anything I've ever had.

I look forward to looking into the sources you guys have provided.

whart wrote:

None of the Zep albums are in my view of audiophile quality-- it is somewhat sad, given the significance of the band, that they weren’t able to put together better quality recordings.

I came late to LZ (1978-ish) and even though never an audiophile I kind of got that impression even back then. They seemed to have other priorities than production value whereas with Rush, Floyd and others, production seemed to be very important to the band.

You may also want to peruse The Absolute Sound's Super Disc list.  It is a quite extensive listing of superior recordings of both the symphonic, jazz and popular categories.