All UHF wireless systems that I checked can not use both
lavaliere and handheld simutaneously, i.e. only one device
can be used.

In my situation, I need to take at least one lavaliere and
one handheld sound inputs at the same time to my XL2.
Of course, I can use two wireless systems since XL2 has
two XLR inputs. Or, I can use a portable mixer.

What I am wondering is whether there is such wireless system
that can use both lavaliere and handheld (or two lavalieres or
even more) at the same time while just using one wireless
receiver attached to my XL2.

Anything like this?

Really appreciate your kind advices.

There is no such thing like that. The only thing you can do is use a mixer. The number of microphones depends on the number of mic input of the mixer of course. Then connect your wireless transmitter to the output of the mixer. Azden has a UHF wireless that you can use 2 microphones simultaneously with two transmitter and one receiver. Check this out:
http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=383975&is=REG&addedTroughType=categoryNavigation

Thanks.

I saw several Dual Channel one, but they only support two lavalier, but
not one lava and one handheld.

Maybe I can go with just a dual channel system to one XLR input and
the other handheld to the other XLR input ... Mixer seems a better
idea though (expensive solution though).

There is no such thing like that. The only thing you can do is use a mixer. The number of microphones depends on the number of mic input of the mixer of course. Then connect your wireless transmitter to the output of the mixer. Azden has a UHF wireless that you can use 2 microphones simultaneously with two transmitter and one receiver. Check this out:
http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=383975&is=REG&addedTroughType=categoryNavigation

If you get something like the SennG2100, it is not that big a deal to have two receivers.

2 on strap
1 on strap 1 on top
1 on cam 1 on belt (my favorite)
both on belt.
...

That must looks like professionals ... :)

If you get something like the SennG2100, it is not that big a deal to have two receivers.

2 on strap
1 on strap 1 on top
1 on cam 1 on belt (my favorite)
both on belt.
...

the Sony 862 receiver support to channels with 2 transmitters ,
you can hook another unit if you are running 12bit
but - the Sony is a crap for its price and 12 bit/32 kHz sampling is something that i dont think is what you wont
so small mixer which can mix 3 channels to 2 tracks is the way to go

I agree with you. The problem is to find a good dual channel
wireless system. Neither Azden nor Sony is good at sound
quanlity.

Any recommendation of other brands?

the Sony 862 receiver support to channels with 2 transmitters ,
you can hook another unit if you are running 12bit
but - the Sony is a crap for its price and 12 bit/32 kHz sampling is something that i dont think is what you wont
so small mixer which can mix 3 channels to 3 tracks is the way to go

I agree with you. The problem is to find a good dual channel
wireless system. Neither Azden nor Sony is good at sound
quanlity.

Any recommendation of other brands?

Sennheiser, Lectrosonics, Audio Technica

Sennheiser
Lectrosonics
stay away from sennheiser in the high end - dont worth the money

I simply can't find a good dual channel one less than $1500. I saw
a few and listed below:
Audio-Technica AEW-5313 Dual Wireless Condenser Microphone System $2500+ (and AEW 5111 $2300+)
Shure UHF Series - Wireless Dual Microphone System with U4D Dual Diversity Receiver and Two U2 Handheld Transmitters with Beta 87C Capsules (UA) $2600+

How about Lectrosonics? I have never used this brand before. I have AT, Senn, and Shure products and tried Sony and Azden as well.

Sennheiser, Lectrosonics, Audio Technica