I shoot twice a month at a venue that has an XLR input on the wall. The venue uses THEIR wireless audio, puts lapel on speaker and uses 2 handhelds, plugs receiver into this XLR input. If I had a y-splitter off the back of their receiver, sent one cable to their input on wall and sent the other cable to MY wireless transmitter, should that work ok? Of course I would check frequency's, but I guess my question is "how bad is audio degraded when splitting"?

I have been adding my lapel and transmitter to the speaker (now he is wearing 2) but the bigger problem is capturing when the intermittently also use the other 2 handheld wireless mics. Its a long story and not an ideal situation, but I have no access to the sound room, only this one XLR input on the wall that they always use for the wireless system.

A simple Y split should be fine but to do it properly and to isolate your equipment a transformer mic splitter box would be better, it would also allow you to safely ground lift to remove any hum problems.

Art make several boxes as well do other manufacturers, note it will change the levels very slightly.

What Gary said. I've found this useful:Rolls MS20C Splitter/Combiner/Isolator MS20C B&H Photo Video (http://www.bhphotovideo.com/bnh/controller/home?O=&sku=356436&is=REG&A=details&Q=)

Without such a device you are almost guaranteed to have a ground loop.

A transformer mic splitter is your safest/best bet. If there's Phantom Power involved, the supplying mixer should be on the 'direct' output, the secondary mixer on the transformer out and it's Phantom Pwr. turned off.

The venue uses THEIR wireless audio, puts lapel on speaker and uses 2 handhelds, plugs receiver into this XLR input.

I'm a little confused about what's going on here. Are you saying the venue has a wireless lapel, PLUS two additional wireless handhelds? If so, and if all three of those mics are on at the same time, they would need three separate receivers to receive the three different radio signals.

Can you clarify this, please?

I'm a little confused about what's going on here. Are you saying the venue has a wireless lapel, PLUS two additional wireless handhelds? If so, and if all three of those mics are on at the same time, they would need three separate receivers to receive the three different radio signals.

Can you clarify this, please?

Hmm, good question. What I ASSUME is this, the 2 handhelds must be hardwired somewhere, probably in the A/V closet that they don't seem willing to grant me access to. When they attach the lapel to a speaker, they enter the room with a box, pull out a lapel and receiver, then plug the receiver to this XLR wall plate.

Many wireless receivers also have a 1/4-inch unbalanced line-level output in addition to the XLR output.
You could use this output if the receiver has one, but you would still need to isolate it by using a passive DI box with the ground-lift switch engaged to protect from ground loop hum and to balance the feed over the long XLR cable to your recorder.
Rolls also makes a nice, inexpensive DI box (DB25b) with a rotary attenuation control to dial in a good level being fed to your recorder.

Just wondering what wireless system the venue is using, and if you could grab their signal out of the air? You'd need an appropriate receiver of course.

Just wondering what wireless system the venue is using, and if you could grab their signal out of the air? You'd need an appropriate receiver of course.

An XLR cable and DI box would cost a whole lot less than a professional grade wireless receiver.

And you could use the XLR cable and DI box for something else.