Once you've finished building an AV system, there are several additional pieces of gear that are worth investing in to maximize its performance.
Here are 5 items I strongly recommend you buy as soon as you're done setting up an AV system, and that I use within my own system at home.
IsoAcoustics Isolation Feet
Uncontrollable vibration is bad. For products like a CD transport, turntable, video transport, and speakers, vibration can smear stereo imaging, creating boom-y bass, and less intelligible vocal/dialog. Adding an isolation platform, however, cannot be done haphazardly. The equipment weight and the absorber should be matched perfectly (within certain tolerances). Using spikes, high density foam hockey puck-like devices can help to a certain (minimal) degree such that unless you have trained ears, you may not be able to hear the difference.
With IsoAcoustics, however, you can choose which feet you should buy depending on the size and weight of your equipment. In my case, I use the ISO 130 ($110/pr) for my bookshelf surrounds, Aperta 300 ($240 - shown in the photo) for my centre channel, and Orea Bordeaux ($100 ea., total of four needed) for my subwoofer. The results? Immense widening of the surround sound stage, and the same level of bass kick minus the rattles in my theatre (yes, it reduces physical rattles in my room). Dialogue is also so clear that I can hear the widening of the front stage, too. There is nothing subtle about what IsoAcoustics can do to your system.
FCUK Labs Super Ground Box
I have to admit, this products sounds like its a voodoo audio tweak. But these handcrafted boxes (US$250/pr. with US$80 shipping - they are heavy!) can lower your system's floor noise by as much as 15dB (measured).
The results? While it is system dependent (I can't hear any difference using this in my 2-channel system but I can hear improvements in my dedicated home theatre), there are noticeable differences in openness and solidity in the lower-mid frequencies. It's subtle but clear. If you have done everything you can to better your system, get these boxes as the finishing touch to polish it up, and allow it to reach maximum capability.
IOGear 4K Wireless HDMI Extender
If you are like me, you have your entire AV machinery in a separate room. Gaming, though, can be a hassle. Many gaming consoles (especially the retro ones) require that you run HDMI cable from the viewing room to the equipment room if necessary. But that can be a messy proposition.
With the IGear 4K Wireless HDMI Extender (US$250) I can now enjoy gaming using my home theatre without needing to run a wire to my equipment room. For testing, I used my Super Nintendo Classic playing Donkey Kong Country, along with several other games through my Playstation 3. I didn't experience any lag, and there was no drop out, even when I put the unit three rooms away. That's thanks to the 60GHz wireless band it uses. If you need the 4K movie experience with full 18Gbps transmission, a UHD/60Hz option is also available for US$600.
iFi AC iPurifier
These active noise suppressors work by analyzing the incoming electrical signal and creating the reverse polarity to pretty much cancel out noise completely. It helps with most with analog systems, like a turntable and amplifiers. Depending on the original noise level, you can use multiple units to get rid of EMI and RFI interference that gets embedded into your electrical system, depending on how dirty the power is to begin with.
In my bedroom, two of them helped clean the slight buzz I typically hear from my turntable and sound platform. For my living room, with the power filtered using a Furman power conditioner, I used two Purifiers to clean the faint buzz from my ZVOX sound platform. In my home theatre, where the power has been cleaned with a Torus Power RM15+ isolation transformer, only one was needed for my turntable since the electrical noise floor is almost non-existent to begin with.
For something that is only $150 ea., I recommend you use at least one and plug it in nearest to your turntable (if you use one) or amplifier/receiver (or active speaker/soundbar). Buy a second one if you still hear any remaining noise.
AC Infinity AV Cooler
Heat is a silent killer for any electronics gear. It is one thing for an amplifier to run hot, but an AV receiver should never be. The heat will kill other components within the receiver. That's also the reason you should never put any other equipment above your receiver or power amplifier. However, with limited space, sometimes that is simply impossible. Just like with my equipment rack.
Thanks to this cooler (I bought the Aircom S6 from Amazon.ca for $90), the heat from my receiver can be sucked up and then thrown to the back of the rack so I can put another piece of equipment right above the cooler. You can set the fan speed for continuous operation (I set it to run on low at all times), or use the automatic setting so when the thermostat senses a certain level of heat, the unit automatically turns on and does its job.
You can also choose a version that blows the heat to the front of the rack, or even blows cool air inside the equipment, though I wouldn't recommend that as it introduces dust into the equipment.
If you only have the budget to do one upgrade this year, I'd go with the IsoAcoustics isolation feet - regardless of how great you think your system already is.