Tvheadend

If you have linux firmware for the tuner and the kernel accepts it, I don't think so.
How much tuners do you want to use? :O

Dunno.. More than two. I have one presently, but that is one that supports both DVB-T and DVB-C. I was thinking of adding at least two more to be able to record several channels across muxes, simultaneously.

That will definitely work!
Once I had 5 usb dvb-t tuners. Now I have a dual dvb-s and a single dvb-t tuner.

What tuners (make/model) did you use for DVB-T? I have a PCTV tripleStick T2 (23076) that does both T and C, but I could probably use something cheaper for DVB-T

Cheap eBay Realtek RTL2832U+820T DVB-T tuner, and now iT9135 rev2.
But I can't tell you which firmware the 9135 uses. The firmware from openelec repo or the ljalves one.

Great! I had one on order from China, that took ages to arrive, but it did so today. A DVB-T + DAB + FM Radio Realtek RTL2832U R820T software defined SDR HDTVwbGT15. Possibly the same as you have. Plugged it in and currently recording two muxes at once. The cost was close to nothing so I might order a few more

I have two dual tuners Evolveo Venus and some AverTV tuner. In total 5 tuners.

But beware, for example two Evolveo Mars tuners works on x86 platform but does not work on mips platform. Driver has some error, same kernel version but different platform.

Good to know. I guess this really should be put in the Wiki, here or on LinuxTV?