I had been using symphony in USB mode for many years with no any issues, however after I updated the OS to 10.9, the Maestro doesn't work as stable as when I was using 10.6.8, and then I tried 10.10. No luck. It just sometime keeps loading there or no response at all, I get to restart the computer or the symphony to make it working again. Maybe the only way is to get a new Mac with using the ThunderBridge to solve this issue.
For the USB cables, I know it doesn't make sense for some of you guys as I did, but I really hear the difference between the stock cable and the one where I just bought in a computer accessory store since I need a longer cable run but the length is limited in around 12'. So, I got it and tried. I'm not trying to say which one better, but at least I really hear the difference with different USB cable.

From what I can tell, you're definitely going to have to update the drivers and the firmware from Apogee's website. Easy fix. As for the USB cable sounding different, I'm not to sure if that's really possible, but hey sometimes our ears like to trick us into thinking something sounds better. Who knows, maybe you are getting some signal degradation because of quality control or who knows what. On another note alternative4, what buffer size are you running in USB mode? How many plugins or Virtual Instruments can you run without problems? What are your systems specs? I seemed to do good with the USB mode, and the thunderbridge is supposed to lessen CPU usage, but from my recent trials (granted, which have not been many) it seems to be no help. Thanks!

I updated the OS with both of the symphony driver and firmware, the problem can't be solved. The computer is a pretty old 07 iMac which was enough for me to record 16 drum tracks at time with 64 buffer size, 24/48k and a simple rough mix with no any issues while using 10.6.8. I usually have to freeze all the Virtual Instruments and just add some plugins for the audio tracks. However after I updated the OS, it's not as stable to do what I could. I did it because of the new switchable monitor function in Maestro but now I regretted updating the OS and not sure if I can downgrade the symphony's firmware, so I guess it should be easier to get a new faster computer to solve this problem. If I have the option to use thunderbolt or usb, I would probably go for thunderbolt which performs lower latency.

Hm. Strange. What are your specs on the iMac? From the sound of it, my computers are both much faster but it sounds like you can run more plugs and tracks than me! What the hell! Well I'm using the Thunderbolt, and the latency is undoubtedly much better than the USB. What exactly are you using Maestro for? What DAW are you using? For the most part, I just load up whatever DAW i'm gonna be using for that project, and anything that needs to be set up or controlled can be done so through the daw or with the front panel of the Symphony. So if Maestro is giving you trouble, just don't use it I guess. I can't really think of any reason why it wouldn't be working like it used to. My suggestion is this:

1. Uninstall the Maestro software and the Apogee drivers completely (there's an option for this inside the .dmg file that you download the latest version of from the website). Then reinstall it all, if you're on 10.10 now, make sure you're using the 10.10 installer and double check if the firmware is up to date.
2. Double check that on the front panel, when you press the right-hand side button, you are set to USB. I had accidentally set mine to standalone one day without even noticing. Took me forever to figure out that I just had it in the wrong mode.
3. Sounds stupid, but double check your cables. With the thunderbridge, my PC32 cable was a little loose and I spent hours trying to figure why the symphony wasn't connecting to my mac in thunderbridge mode but was in USB mode. I know you're using USB mode, so double check you're cables make sure the connection is clean. If you're using that longer cable you said you bought, switch it back to the Apogee-included USB cable and test it out and see if you're still having problems. That may have something to do with it.
4. If nothing is working, power-cycle the Symphony and the iMac. If no luck there, call apogee.

I'm on studio one 3 and bitwig (logic seldom), been happily using usb for a year then got thunderbridge a week ago. I'll probably send it back bc I haven't seen enough of an improvement and my 2012 mini has rebooted randomly (black crash window) twice since only that upgrade. I went back to usb and no reboots. usb was super solid and I was happy enough with the performance. Same thing with kontakt and amplitube for me, with thunderbridge I still have to turn off hog fx to track guitar after getting into a song...I'm running latest maestro etc.

Jimmy,

After posting, I did however run a full test of how much of a load the thunderbridge was assisting with due to my skepticism. However, I was pleased with the fact that although it doesn't seem to do much good with cpu hogs like amplitude and large sampling libraries like contakt, I noticed that my MBP could handle many more audio tracks playing all at once then without the thunderbridge(total of about 50-60 at 32 buffer with no drops or pops). I also noticed the same thing with more instances of less intensive plugins such as simple EQs, Comps, Convolution Reverbs, modulators and hardware emulators. This carried over to my main computer, which is a mini as well. The improvement is there, but just not as helpful on the really troublesome plugs.