Since switching to Windows 10 from Win 7 Pro 64, I've been experiencing playback dropouts regularly.  The sound will just glitch for a sec then come back on. Never happened on Win 7. My buffers are both set now at 1024, and this doesn't seem to help. Doesn't happen all the time, but often enough to be a major peeve. 
I've closed all my browser windows just to see if that helps, and no it doesn't.  
According to my resource monitor, I'm using about 20% of my CPU power and around 30% of my ram.  Not a big machine, but quad core, 3.1G, 12G ram.  Shouldn't be a problem...   any ideas?

Are you on line, try shutting off your internet connection, Windows 10 does huge updates and it's next to impossible to disable this feature now. Also make sure there is not a lot of background processes happening. Run Latency Monitor.

Did you grab the Windows 10 driver for your interface.  I 'm not certain W10 automatically grabbed the new drivers for the interfaces.

are you using a wireless network ?
turn it off in device manager. see what happens. (possibly interference)

Upgrading to Win 10 can be like getting a new PC.  Bottom line, you may need to recheck all of your audio-related settings.
 
Try a different USB2 port (Avoid USB3 ports).
 
If still a no-go, run this to maybe get a clue as to what is causing the issue.
 
http://www.resplendence.com/latencymon
 
 
 

I recently went through similar problems when going from Windows 7 to Windows 10 with a Focusrite Scarlett 18i20.  Focusrite's tech support worked with me to solve the problem.  They had me try all their beta drivers and Mix Control software, but nothing worked until I updated the firmware on the interface.  When I initially tried to update the firmware, it kept failing, and tech support couldn't tell me why.  They said they'd had issues when updating the firmware using a Windows computer and wanted me to try it on a Mac, which I don't have.  They wanted me to ship the interface to them so they could update it.  I decided to try using my wife's Windows tablet, and for some reason it worked and after that everything functions fine.  I don't know if there is a firmware update for the 6i6, but it might be worth looking into.

Cactus Music
Are you on line, try shutting off your internet connection, Windows 10 does huge updates and it's next to impossible to disable this feature now. Also make sure there is not a lot of background processes happening. Run Latency Monitor.

where do I find Latency Monitor ?

chuckebaby
are you using a wireless network ?
turn it off in device manager. see what happens. (possibly interference)

no wireless

are you running the X3 update (X3 E) ?
 
Also make sure to check and see your driver mode is set to ASIO (what you should be running for your Scarlett)
you have the mix control software correct ?
 
this is probably related to your driver problem as I remember a few posts in the past about you having issues with the scarlett drivers.
I would un install and re install them again. make sure your not in a usb3 slot first and for most.
make sure you have a driver supporting windows 10.

OK,  I watched a bunch of youtube videos on how to speed up Win 10...   made a bunch of changes re. startup and background apps, ran CCleaner which cleaned up lots of things, and playback seems to work ok now on the 1024 buffer setting. But when I go to 512, it starts to glitch again.  Is this normal or acceptable performance?  
 
My boot time is like 2 minutes or more, or something ridiculous like that, up from around 40 seconds (at a guess) on Win 7. This is after eliminating practically everything from my startup menu.
 
I can still revert back to Win 7 for a few more days...   wondering if I should. I have a brand new (non-VGA) hi def monitor, and the brand new 6i6, wondering if I'll just be asking for driver problems going backwards...   any of you guys revert back to Win 7? Everything worked just fine on 7!