Ok I just installed a pvr-150 in addition to the 250 I already had. Went well except for one small issue, the volume on the 150 is significantly lower than the 250. So after a few searches I discovered you can adjust the volume levels of the cards via the ivtvctl command. My 150 was set to volume 52224, I used the following command:
ivtvctl -d /dev/video1 -y volume=58880
and lo and behold the volumes match.
But as soon as you exit the playback and invoke the card again mythtv sets the volume back to 52224. From my searches it looks like this is set via the recording profiles.
Is there a way to make this volume setting stick? I found a post to the mythtv users list from 4 months ago asking this same question, with no replies: http://www.gossamer-threads.com/lists/m ... ers/148311

So I'm not too hopeful if no one on the mythtv users list could answer the question, but then again I've found this forum to be much more helpful and friendly than the mythtv lists. So let me know if you have a solution, I think maybe it could be done with a channel change scrip but I don't know enough to say for sure or set that up. Thanks a bunch!

This may help...
http://ivtvdriver.org/index.php/Troubleshooting#Multiple_tuners_have_very_different_audio_levels
Especially if you combine it with an "external tuner" script that makes the appropriate adjustments to the sound level and then the channel using ivtvctl and ivtv-tune respectively.