By "pro CD" what are you referring to?

As far as formats go, it all depends on what you're looking for.

First off, the CD format is what it is. It's a 16-bit format sampled at 44.1 kHz. HDCD is an enhancement that purportedly provides a slight increase to the dynamic range, but you need both a HDCD-encoded disc and a CD player capable of decoding the HDCD data.

Aside from SACD, the other high resolution digital audio format out there is DVD-Audio, which is a 24-bit audio format that uses sampling rates of 96 or 192 kHz. SACD and DVD-A are both considered failures because they never really gained a huge foothold in the market. Several releases did come out in both formats, but the major labels have slowed down their releases to a trickle. While both formats did provide higher resolution, IMO the biggest benefit that they brought to the market was 5.1 multichannel audio. Multichannel necessitated remixing the original multitrack masters, which often resulted in a noticeable improvement in audio quality. Plus, you get a very different listening experience with the music in surround.

There are also DVDs out there listed with "PCM Stereo" tracks. The DVD format natively supports higher resolution audio, and these PCM tracks can actually go up to the 96/24 resolution that DVD-A uses (except that it's limited to two-channel). DVDs that include PCM tracks are typically encoded at lower resolution to make space for the video data, but still higher than the CD's resolution.

In addition to these uncompressed (or "lossless") formats, you also have Dolby Digital and DTS, which are both compressed formats. Both are capable of 5.1 multichannel audio (with DTS ES capable of 6.1). DD is the more compressed of the two formats and one of the standard audio formats for the DVD. DTS is less compressed, and is an optional audio format for the DVD.

But, no matter which format you're listening to, by far the biggest variable is the original recording itself and how the transfer was done. If an original recording was done poorly, it won't matter if you're listening to a CD or SACD, it will still sound bad. Conversely, a well done CD can sound quite good in its own right. While a high res SACD or DVD-A version will often sound audibly better than the CD version, keep in mind that the differences between the two versions go beyond just the playback format and resolution. Different mastering engineers might have been used to supervise the transfer from the master tape to the CD/SACD/DVD-A, using different EQ or processor settings, different playback rigs, and even different master tapes. It really comes down to a case-by-case proposition.

Which player you go with depends on whether you really want to explore the high res digital formats. And in that respect, you should look into what titles are available in both formats, and see if any essential albums are in DVD-A and/or SACD. If so, then it might be worth looking into a dedicated CD/SACD player or a universal DVD player that plays SACDs and DVD-As. If not, then stick with a higher quality CD player (some of which will have HDCD decoding on board) and be done with it.