RabPaul

The mini has a built in switching power supply and to get the best out of it means replacing it which is not inexpensive. Having said that there are many Mini users quite happy with the Mini as is. If you used a thunderbolt drive on the Mac you would be fine. Is your MacBook Pro very old? Why not use it instead of buying a new Air or Mini as SSD does not give you much of an advantage as Audirvana will use memory play anyway.

You mention Raid5, the best practice (ask any IT professional) is to use identical drives, perhaps this explains what you are hearing.

My cable choices are based on reviews balanced with what I can afford. When it comes to power cables I have set the arbitrary limit to 25% of the cost of the component. I know of audiophiles whose power cables cost half or more than the component it's connected to, which is something I think is daft.

I believe every audiophile is a closet reviewer i.e we have out own opinions on everything related to our hobby. Now the question is are we going to voice our opinions or do we succumb to peer pressure. Let's say you, with a bunch of audiophiles visit and listen to a system, would you voice your opinion if you think something is not right or would you keep silent when everyone else thinks this system is bloody good. I will even say expressing your real opinion or doubt is a lot easier when you are faceless, behind keyboard i.e no peer pressure. Media players don't sound the same? I have A+ and Amarra but it does not mean someone is wrong because they could not hear a difference as some systems may not be able to resolve that difference for a myriad of reasons. I don't see this being related to peer pressure at all. USB cables do sound different. Honestly I have taken the general consensus on this based on the USB cable reviews I have read. I bought the best USB cable I could afford and left it at that. I won't try to convince anyone that they make a difference or even prove it to myself that they do, much like they way I have accepted that interconnects do sound different. To me this is commonsense as the signal going through is after all analog (albeit representing digital data) and some of same reasons that make interconnects sound different apply. Again I don't see this related to peer pressure at all.

Get the Forest or try out another cable (which you can return) and compare it with your stock cable. It's just prudent to determine how much of an effect a "better" cable has in your setup than to assume an even "better" cable will produce even better results.

You don't mention which power amp you are going to use. I would think you would need to determine which pre will go best with your power amp e.g impedance matching i.e getting the best output/input impedance ratio possible especially when considering valve pre/power combinations and you are mixing brands.

The only way to be convinced is to prove to yourself one way or the other rather than to rely on proof that it makes a difference or does not. If you look at the audiophile grade USB cords you will see that many of them place emphasis on the material and isolation used for wires that carry the data as well as the how they isolate the wires that carry the power from the wires that carry data. One theory says the power signal (let's not forget EMI/RFI) can corrupt the data signal turning what is supposed to be a zero signal to a one signal and vice-versa. Now the effect of this if any, will also depend on how capable your system is in resolving these differences again if any. As mentioned by others you may well be hearing things because you want to hear them. The only way to know if these "differences" are real or created in your mind is to actually try a standard USB cable with an "audiophile" grade cable. Try an inexpensive USB cable say from DH Labs, Audioquest or Cardas and use the standard cable that came with your DAC. Spend a week playing music you are very familiar with using the new cable and take note of the differences you hear, now repeat with standard cable and look for all the differences you noted earlier. Repeat the whole exercise again and decide which cable is better for you. If you are served coffee with sugar you would know when there is no sugar. If the cable allows you to listen to more detail you will know when that detail is missing. So no difference at least you have a good quality USB cable which you will never have to replace.