After giving some though*, I'm planning to build a portable PC (slim ATX case, inside a travel luggage) for the purpose of field recording as well as experimental live performance running Cantabile host, Mobius Looper, etc. with midi foot switch and audio input for guitar and bass.
 
*instead of using Intel NUC, Gigabyte Brix, notebook etc..
 
I'm thinking of i7 4790K instead of i7 6700K based on simple google "vs" check.
 
My main concern is the USB support for my existing Roland Quad Capture - according to the spec, it must run with USB 2 interface, or USB 3 that is compatible with USB 2 spec.
 
Does it mean the USB 3 implementation with Z97 chipset is 100% compatible with USB 2 ?
 
Should I get a board with USB 3.1 - will it be compatible with USB 2 / 3 ?
 
Thanks!

Most of the boards I looked at have both -- USB2 and USB3 ports.  Unless you're looking at a specific board (that only has USB3), I don't think you need to worry about this.

What do you think of Gigabyte board ?
 
With reference to :
https://linustechtips.com/main/topic/235201-low-dpc-latency-z97-board/
 
The MSI Z97 MPower Max AC seems beyond my budget.
 
The Gigabyte Z97X UD5H seems to perform quite good, at a budget that suits me and having good count of USB 2 ports.
 
http://www.newegg.com/Product/Product.aspx?Item=9SIA1N83WB8575&cm_re=GA-Z97X-UD5H-_-13-128-707-_-Product
 
From reading reviews, it seems there are 2 kind of USB 2 implemented on the same board :- Z97 chipset and some sort of Hub (in Gigabyte case it's Renesas HUB). Should I be strict about plugging the audio interface only to the chipset supported USB 2 ports ?
 
Thanks!

tomixornot
Should I be strict about plugging the audio interface only to the chipset supported USB 2 ports ?

Interesting question, and I think a very important one.  Yes, it's probably best to do so for your interface. (It really doesn't matter for the secondary peripherals like mouse, keyboard, etc).
 
Having said that, I never worry about this issue because I've always installed an add-on PCI/PCIe USB2 card for the audio interface (Same for Firewire).  The PCI/PCIe bus gives you all the bandwidth you'll ever need, and I've never had any USB/interface-related problems with any of the past 4 PCs I've done this on.

tomixornot
Should I be strict about plugging the audio interface only to the chipset supported USB 2 ports ?
 

Z97 motherboards that offer USB3.1 - the USB3.1 ports are provided via PCIe controller (3rd party).
Many audio/MIDI interfaces have issues when connected to 3rd-party USB3 controllers.
Liken the situation to using a non-TI chipset Firewire controller with a Firewire audio interface.
 
As to your question:
It depends on the specific audio interface... and the specific USB3 port.
Using Intel USB3 ports (controller integrated into the Intel chipset - Z77, Z87, Z97, Z170, X99) your odds of success are much higher.
 
BTW, If your motherboard has few/no USB2 ports:
Most motherboards have USB2 headers.
You can get a USB2 bracket (less than $10 - resides in an empty slot space) and connect that to one of the motherboard's USB2 headers.  
This will provide a pair of Intel USB2 ports.
 

Great info. Thank you guys!