Do you have USB 3.0 in your windows machine? Try to use that port as, in my experience with windows 7,  USB3 gives less CPU usage than USB2, due to some windows Microsoft drivers issues for audio through USB2.  I had some periodical CPU usage spikes when USB audio card was conencted to USB2.0, this caused audio pops/breaks during the playback, when I put the card to USB3.0 (NEC/renesas) port CPU spikes vanished and audio stream had no pops/breaks....

Set the power scheme to "high performance" in "Control Panel / Hardware and Sound / Power Options.
You can also try to increase latency in windows to see if it helps, with babyface I use 128 samples, you can try 128/256 to see if there is a difference.
Disabling Network (ethernet/wireless) adapters might also help to reduce audio issues as those adapters very often introduce the Deferred Procedure Calls latency to the audio streaming...

Gregor,

thanks a lot for your help and ideas!

Unfortunately there is not USB3 in my machines. I will install the drivers tomorrow on one more MacBook Pro, which has USB3 ports, we'll see does it changes things to better. I already did all the Win 7 tweaks on my DAW computer before some years, using it daily with no crashes and problems at all with eHDSP AES card. But may be the motherboard is too old for this new product, who knows. Latency checker said my system should handle real-time audio without problems (as it really did before).

My concern regarding USB2 vs USB3 is valid only for Windows, only there were some issues for audio on USB2. For MAC machine with OSX you will not see any improvement from USB2 to USB3 as Mac OS does not have any issues with USB2 audio and your card will rather not gain anything as it is USB2 card. Regarding lack of  problems for eHDSP, PCI cards are less CPU consuming than USB thus they are less demanding for computer.  For Madiface in Windows You can try different USB ports, as the best is  to use USB controller for audio interface exclusively, not sharing it with any other USB device ( like mouse/keyboard or pendrive)  It is well described in all RME USB devices manual.

Look at Madiface USB manual (page 64):
"While the MADIface USB will work on older computers with for example a Core 2 Duo CPU and ICH 9 as USB hub, the CPU
load is noticeable and DPC is raised from the underlying USB driver of the operating system.  Newer computers, especially those already having USB 3 ports, usually show no such issues, as their raw performance handles the USB load with ease.
(...)
Like any audio interface the MADIface USB should have a data transmission to the computer as undisturbed as possible. The easiest way to guarantee this is to connect it to its own bus, which should be no big problem as most USB 2.0 interfaces are a double bus design. A check in the Device Manager can be done as follows:
- Connect the MADIface USB to a USB port
- Start the Device Manager, choose View Devices by Connection
- Select ACPI x86-based PC, Microsoft ACPI-Compliant System, expand PCI Bus
This branch normally includes two entries of a USB2 Enhanced Host Controller. A USB Root Hub can be seen, which then connects all USB devices, including the MADIface USB. By reconnecting to a different port this view now allows for a check at which of the two controllers the MADIface is connected."