¿Could you be more specific? As a general advice, my current setup works flawlessly with Logic Pro X, running more than a hundred benchmark tracks.
The i7 4790K is probably the best choice if you want power without leaving the Z97 architecture, but unless you run very demanding projects, you can buy an inferior i7 or even a powerful i5 if you are on a tight budget. You might want to check some benchmarks, but a 4790K might be overkill depending on your needs. Also, if you don't plan on overclocking you can save some money by buying non "K" versions. Stock coolers provided by Intel might be cool enough for you, but they can get quite noisy for a DAW build. I bought a Noctua NH-U12S to keep the CPU cool and silent.
I bought a Gigabyte GA-Z97X-UD3H because it was fully compatible, reviews say it's well built and reliable, and I didn't care for the extras of the higher mobos. It has no bluetooth, wi-fi or firewire, so take that in mind. If you want those features you can buy a mobo with them (check for compatibility with OS X, because they tend not to be) or buy separate PCIe components. I bought this for FireWire: http://www.tonymacx86.com/buying-advice/59767-firewire-800-400-card-own-100-compatibility.html
RAM is cheap, so you can go with 16 GB to be sure, specially if you work with video or other heavy material. It should be DDR3 and it will perform better if you don't cut corners with speed. 1600 MHz is just a few dollars more expensive than the slower ones. Mine is 1866 MHz, but OS X seems to lock speed to 1600 MHz, so that's the speed I recommend. Dual channel performs better than single channel. This means it's better to have 2x8GB sticks than a single 16GB one. If you think 8GB is enough, don't be too afraid to go with it. You can always add more as long as your mobo supports it.
If you don't plan on gaming or working with video, you can probably go without a discrete video card, as long as your CPU has a decent integrated card. I use a Gigabyte Geforce GTX970 G1, but if you are interested in saving some money, I can run any task you want with my integrated CPU graphics and tell you how it went. Also, keep in mind powerful video cards can add a bit of fan noise even when not at 100%, but maybe using the integrated video would make the CPU get hotter and causing the HSF to make more noise. Not sure about what would be louder.
I would totally recommend an SSD for OS X and maybe sample libraries and the current project you're working on. You can store finished projects and the rest of your data on a conventional HDD. I have a 256GB Samsung 850 PRO SSD and it's performance is way better than a HDD. An SSD is probably the best bang for your buck nowadays, even more for audio computers. Also, you can finally use TRIM on OS X 10.10.4 or newer without third party apps. There's also the option to combine an HDD and an SSD on a Fusion Drive. In theory this means OS X automatically puts the most used files in your SSD and the rest on the HDD, appearing as a single volume. This should give you the storage capacity of an HDD with way faster speeds, but I haven't tested it.
Finally, I choose a Corsair Carbide 330R case. It's easy to build, nice looking and it has some noise dampening foam on the inside. I was afraid that would come at the expense of cooling, but I've been working with it this summer in Spain and it keeps things cool. It also has a fan speed controller, so you can keep noise low. As for the PSU, getting more power than you need means it doesn't have to work to the limit, so it doesn't get so hot. This means it will be more reliable, lasting and less noisy, as PSU fan won't have to be running so fast (you can even buy a PSU with zero RPM fan mode which deactivates the fan when it's not necessary). It will also mean you won't have to upgrade it if you buy new components (like a video card).
If you have more specific questions, feel free to ask.
