Steinberg WaveLab is serious mastering software for any level of engineer. It's super-fast and incredibly powerful, has worked flawlessly for me for years, and now I can even run it on my Mac!
It's the venerable Wavelab!
I've been using Wavelab since Wavelab 3. I have loved this useful program to Master underground recordings to compete with the larger Mastering houses who must make a living and pay the bills. Wavelab has always proven to be the best Mastering tool I've used for less than $1,000! (Even less than $3,000!!). If I had one piece of software to give you to master a recording to CD-RedBook or MP3, THIS IS IT! The metering alone makes it worth the money. Add in the abilities of coding, now exporting as DDP, and a great editing GUI, we have a winner.
I have used Wavelab before to mix 50+ track sessions just to see how well this could be done. It was very doable, but not quite as easy as other DAW's. Wavelab 7 is primarily a Mastering/Finishing tool, and does a very nice job!
With all this said, I do have some gripes with Wavelab 7 vs. any of the previous versions. This supports 64-Bit systems, and MAC OSX (although you have to purchase version-specific), which is nearly a requirement these days. I wish it had an option to emulate the previous GUI's in Wavelab 7. Mainly, many things you could do or manage in Wavelab 6 were really up to you. You could make your experience as simple or complex as you wanted. Wavelab 7 gives you those options, but not with as much flexibility. The software is very determined to do make a lot of your decisions for you, and remove the flexibility you had in Wavelab 6. Albeit, there's some really cool options in 7, the GUI gets confusing REALLY FAST! I've developed the opinion that many things I wish to do in Wavelab 7 vs 6 is really Steinberg's way or the highway. I don't feel the love nearly as much. Even after 6+ months with the product, I still can't find some functions quickly, and really, just require a LOT of training, where I didn't require much in Wavelab 6. READ THE MANUAL! Spend some time with the product and really dig into it. Learn keystrokes! I'm not a keystroke guy at all, but to make Wavelab 7 work for me, I had no choice but to get good at them. The menu structure hasn't improved any---meaning, it was a disaster before, but hasn't improved. It's still hard to find what you're looking for (much like famous photo-editing, illustrating, and publishing tools tools from a well-known brand) unless you take the time and get to know the product. Intuitiveness isn't 100% Steinberg's strongsuit, but I can quickly and honestly say, more expensive products can be way worse in that regard.
One major gripe I have is that in Wavelab 6, you could remaster a song to the same previous filename and overwrite it, merely by using a simple drop-down selection. In Wavelab 7, you can still do this, but you need a Windows File Browser open to recall what that darn filename was. Wavelab 7 recalls previous working directories, but not the filename. Errr!
Despite some frustrations I've had with Wavelab 7, I still swear on it, I love it, the upgrade from Wavelab 6 was well worth it, and some of the metering etc. has improved. The Master Section has drastically improved, and so has some of the other tools, such as fade-ins and outs, etc.
Give it a go, and you'll be pleasantly surprised how well-put-together this program is, especially from such a small group of people working on it (much of it the work of one man, I understand).
NOTE: Wavelab 7.2.1 version for me has an issue with some 32-bit plug-ins. If you run the latest version, persuade your plug-in developers to natively support 64-bit plug-ins.
We master outside the box, but always to Wavelab for assembling CD's. Wavelab gives you the tools to add an outside produced track into your project and make it fit in sonically. We have even used the multi track for producing radio commercials, etc. on a moment's notice. Been using Wavelab from the earliest versions. Definitely get Wavelab, and the best sound card you can buy.