Unless I'm missing something, running 'apt-get -f install' (as noted in the error message you've posted) should resolve the issue. There is a possibility that you may need rerun the dpkg line, although I'm pretty sure that in more recent Debian versions that isn't required. TBH I would have expected it to "just work" without requiring anything further than the wget and dpkg lines (although obviously that's not the case...).

Unfortunately I don't have a v14.x appliance handy but I would assume that the running the apt-get with the '--fix-broken' switch ('-f-' is the short option) would resolve the issue. If that still fails, then it may be worth trying an 'apt-get update' and rerunning 'apt-get -f install'.

I.e this should do the trick (you can likely skip the first 2 lines; and assuming Webmin v1.900):

wget http://prdownloads.sourceforge.net/webadmin/webmin_1.900_all.deb
dpkg --install webmin_1.900_all.deb
apt-get update
apt-get -f install

Having said that, whilst doing some research to double check my understanding of how it should work in more recent versions of Debian, I discovered that 'apt' can install downloaded deb packages itself in newer versions (should work in v14.x; but definitely works in v15.x). Note the use of 'apt' - not 'apt-get' ('apt' is a newer front end that is designed to be more user friendly). I haven't tested this, but according to my research, the following should work OOTB:

wget http://prdownloads.sourceforge.net/webadmin/webmin_1.900_all.deb
apt update
apt install ./webmin_1.900_all.deb

The error is

Error while processing /etc/awstats/awstats.conf
Error: SiteDomain parameter not defined in your config/domain file. You must edit it for using this version of AWStats.
Setup ('/etc/awstats/awstats.conf' file, web server or permissions) may be wrong.
Check config file, permissions and AWStats documentation (in 'docs' directory).

My guess is that unless you fixed the previous error (I.e. the missing dependency when trying to install a newer version of Webmin) it's just that issue rearing it's head again. And I assume that the Virtualmin install script doesn't expect it, nor know how to handle it.

Although, FWIW, there is also something else worth being aware of. I've just had a look at the Virtualmin install script. Besides the fact that it configures the repos in a sub-optimal fashion, it appears to also configure the Webmin apt repo too. That may also cause issues (if not immediately, then likely at some point in the future when an upgrade of Virtualmin requires a newer version of Webmin). That is because the TurnKey apt repo (which as you know, also provides Webmin) is pinned to a fairly high number (so TurnKey packages take preference over ones also provided by Debian). So it will never install Webmin from the Webmin apt repo, unless you also adjust the Webmin and/or TurnKey apt repo pinning.