When it comes to the input interfaces of the MUB5, I would recommend Bluetooth first, as the MUB5’s Bluetooth is not only convenient but also delivers excellent sound quality, making it a connection method that is hard to let go of once you experience it.
For the other methods, it mainly depends on what output interfaces your front-end equipment has and what good cables you have. Because often, the difference in sound quality brought by a cable can be greater than the difference in the interface itself.
Speaking purely about the sound quality limits of the MUB5’s input ports, the top position should be coaxial, as it has the shortest internal path; next is optical, which has an additional optical-to-electrical conversion compared to coaxial; then comes USB, which has a USB interface in addition to coaxial and optical; followed by Bluetooth, which is a wireless connection; and finally LINE IN, as analog input is only suitable for older devices that lack all the aforementioned digital output ports.
The above discusses the sound quality limits of the MUB5’s input ports, but if we change our perspective to look at the sound quality limits of the output ports on the source device, typically, the USB output has a higher limit than coaxial and optical, as it is positioned earlier in the signal chain and has greater flexibility.
This makes it a bit complex: is coaxial better or is USB better? I think it still depends on what good cables you have on hand. On the other hand, it also depends on the quality of the coaxial output from the source—if the coaxial output from the source is excellent, then it will outperform USB; if the coaxial output from the source is average, then USB is likely to be superior, especially since the USB interface in the MUB5 is well designed.
Another angle to consider is the isolation from interference at the source end. The most thoroughly isolated is Bluetooth, which is also one reason why Bluetooth connections often sound more relaxed; next is optical, as it is optically isolated; coaxial depends on whether the source output has an isolation transformer; USB connections in the MUB5 also have complete isolation (including ground isolation), which is why MUB5’s USB often performs better than coaxial connections.
You might still be a bit confused, so let me summarize:
1. Bluetooth connection to a phone is the first choice, convenient and sounds great.
2. If you have a player and want to pair it, use whichever port has a cable available.
3. If you have cables for all ports, use the one that is of better quality.
4. If the cable quality is similar, most players should prefer USB connections, as I feel more confident letting MUB5 handle more of the work.
5. If you have a very good front-end and can confirm that its coaxial or optical output sounds great, then prioritize coaxial or optical connections.
6. If the source only has analog output, then there is no choice but to connect to the MUB5’s LINE IN.
Let me share a little anecdote. I often see well-meaning reminders telling me that with such a good device, users should not just connect a phone or tablet, and that they should be educated on the importance of a good transport.
First of all, I appreciate your concern; I know you might feel that such a good device is not being fully utilized. However, my thoughts and philosophy are somewhat different.
I believe that the idea of “educating users” is fundamentally flawed. Users are buying a solution to their problems, not hiring a “parent”. Always thinking about educating users does not come from a perspective of solving their problems, but rather has a bit of a “parenting” tone.
The original intention of the MUB5 is to be simple and sound good. And it has achieved that; it only needs a Bluetooth connection to a phone to sound better than many players playing local music. Since this is the case, why should we be concerned about whether a better transport is necessary? If a good transport is a must, then what is the significance of greatly improving decoding quality to raise its sound floor to a sufficiently high level?
Alright, regarding the MUB5 input ports, if you have any other questions, feel free to leave a comment.