Thanks for reply, but, i'm not sure that I understand you I still don't understand how can I use such devices with Ableton being master?
Meanwhile, I got my AR, and the synchronisation problem is definitely here and it is very serious. I tested it with AR's midi port (via several devices to AR) and usb port (without Overbridge, just via USB driver). The problem is the fact that the Ableton's MIDI Clock Sync Delay that has to be entered is not constant within one Ableton's projects; it changes as I tweak clips and play around in general. So, ok, I understand now that MIDI Clock Sync Delay time is not constant (am I right?) and depends on internal and external plugins and instruments; more external instruments/plugins, the longer delay time (am I right?). But I don't understand why the delay time is not constant within finished project: just tweaking the clips and start/stop will most probably cause the change of delay time; maybe the activation of particular instrument changes it? There are several more things I have to test, such as Virus TI VST plugin, I suspect it causes described instability, if so, nice, i will use it as external instruments via midi ports, but if not, it looks like it is impossible to synchronize Ableton and AR. I forgot to mention that my ableton project usually has several external instruments connected via midi (Blofeld, Nord Micro, Pulse2) and mentioned Virus via usb and its VST application. So, delay compensation option in Ableton is holding all of them tight and synchronized, except AR
Also, there is certain indication that the problem here may be in AR rather than Ableton or used midi interfaces; i'm using lot of Pulse2s arpegiator patches driven with Ableton's midi clock via same midi interfaces, and it works fine (with rare dropouts, but it is OK when live performing).