>> I have two soekris 4801 that feature a 3.3V PCI slot. I'd like to use a
>> sound card in one and a TV card (with the brooktree chip, which is AFAIK
>> the only one supported by NetBSD) in the other. It's difficult to find
>> the appropriate cards, as the vendors don't tell if their hardware use
>> 5V or 3.3V signaling.

Is the slot 3.3V only?  Some boards have a jumper to select 5V or 3.3V.
If you have a photo of the card, you can tell by the keying if it is
5V or 3.3V or either.

> 5V cards are obsolete.

They still sell cards that are 5V only.  Cards with features unavailable
in a 3.3V card.

In the US, analog broadcasts are scheduled to go away soon, by FCC mandate.

If you want a card that can receive digital TV, the only card I could find
with any sort of Unix driver is the HD-3000.  It does ATSC (digital HDTV
and SDTV), as well as traditional analog NTSC, PAL, SECAM, ...  Other cards
are wintel only.  The HD-3000 is 5V only.  Driver source is available (for
Linux).  I expect that the driver could be ported to BSD.

http://www.pchdtv.com/
http://www.hijmans.nl/cx88/datasheet.pdf