Congrats on going the Music PC way, Sidvee!
I have a couple of things to say, but please don't take these as post-fact criticisms or buzz-kill. These are based mostly on my reading and a bit on my own Music PC adventures. I'm completely open to be corrected.
1) I think rud3dawg mentioned that a WD AVGP hard disk was used. From what I've read, these disks are not really suited for error-free playback. They are designed to be used continuously for
recording video in applications such as security camera monitoring and DVRs. They do not have any error-correction.
Details.
A discussion on avsforum
I don't think this disk is at all suited for Music PC use. A regular WD EARS (Green) HDD would be fine.
2) Using a low-power processor & motherboard (or combo) would have helped keep the setup completely silent by going completely fanless. The processor wouldn't need a fan. And if a reasonably airy cabinet is used (the current cabinet is good enough for this), a cabinet fan could also have been avoided. In addition, a PICO PSU could have been used, thereby eliminating a fan on the PSU end also. The power brick would sit outside the case, to boot. Furthermore, I think an i5 processor is really overkill for Music PC duty. But I do know that very experienced members like BHAGWAN use dual boxes with i5 processors to run a JPlay setup.
I run JRiverMC on a very low-power setup (AMD Fusion E350 -- Asus E350 M1-M fanless board, 4GB Corsair RAM, OCZ 64GB SSD, WD Green 3TB, Silverstone SMPS & Cab, Lian-li Fan controller, Lenovo Multimedia KB+Mouse). If I'd known enough before I built the setup, I'd have gone fully fanless (no cabinet fans either), and used a PICO PSU.
In your current setup, with a cabinet like that (looks like a CM Elite 120), I think airflow should not be a problem with a mini-ITX board. PSU-wise, there are SMPS units from Silverstone that are fanless. Depending on availability of height/clearance, there are fanless heatsinks from Scythe (and other vendors, including Silverstone) that will do the job at 0dB. This would leave the HDD as the only moving part in the setup.
Keeping everything the same, if you could replace your current front cabinet fan with a 120mm fan from Noctua with a low dB rating, I think the required airflow and need for silence should be taken care of. If the fan is still noisy for your room, you can always tame it with a fan controller, which will help you dial down the rpms (at the cost of airflow).
EDIT: Looking at the pics posted, there is definitely enough room for a serious fanless heatsink.