I can't really comment further, then, I'm afraid - not having a Synology to hand any more!
On a typical Linux system, I'd say that you need to look to log files, see if the /dev/dvb files are being created, see if the tuners are being initialised (should be, if Video Station can use them), see if there's anything in tvh's debug log (web interface, bottom right, arrows, cogs) or in syslog, see if stopping/restarting tvh makes any difference or tells you more, and so on.
If the system can see the tuners then it should tell tvh about them.