my impression is that running line level into a DI is a bad idea, since a DI expects a high-impedance signal. Although, I actually have often done this in the past using a preamp set at a low level, and it does basically work ok - I'm just thinking the signal may be getting degraded. It's sort of related to my previous post about running a preamp into stompbox pedals, except I'm pretty sure most people aren't using reamps in situations where you're just connecting a stage mixer to a house mixer.

Points taken, and I appreciate the feedback. To explain, the reason I need to do this is only for particular channels where on-stage control is required for inserting effects, and not to have any more control over the sound than necessary. Essentially the same as a guitarist would do (inserting effects before sending to the house), except these channels just happen to involve microphones.

For example, In one case, a vocalist needs to have a specific parametric eq effect (his eq box with a footswitch) inserted into his mic channel (for overtone singing), and needs to turn this on/off as needed. Running an effects loop from the house snake/mixer to his on-stage gear just isn't an option most of the time, so as a workaround we've been using an on-stage preamp (usually at a fairly low level). And it basically has worked through all sorts of large and small systems, but it just seems so kludgey.

I guess it is a trade-off, and it sounds best to always request line inputs to the house (which I hadn't been doing), and with any luck they can accommodate this. If not, then I'm no worse off than I am now ;)

you can use di on a line output
it's the same as a key board output
or just use a pad
the di will sound cleaner
get some good di's they will have pad switches in them
hope this helps