Hi,

I have an audio-techinica At8531 power module (AT8531 Power Module || Audio-Technica US (http://www.audio-technica.com/cms/electronics/36396386c21b22ab/index.html)) and so far I've been using it with a pair of AT831c lav mics. The sound isn't bad but I find these lavs are bulky and heavy. Does anyone recommend an option to these mics that works with the power module I own?

You can have a full-service microphone vendor like Oscar SoundTech wire one of their microphones for your power unit.

Or you could use something like the Rode lav (or headset) mic system which uses interchangeable connectors to fit a wide variety of destination gear.

Do you have a link to the specific Rode lav system you've mentioned? I've typed Rove Lav on BH and this came up https://www.bhphotovideo.com/c/search?Ntt=rode+lav&N=0&InitialSearch=yes&sts=ma&typedValue=&Top+Nav-Search=

Rode Lavalier Microphone:
RØDE Microphones - Lavalier (http://www.rode.com/microphones/lavalier)
https://www.bhphotovideo.com/c/product/730766-REG/Rode_LAVALIER_Lavalier_Microphone.html

It is the size of a match-head. And with a cable that is detachable and replaceable in the field.
Furthermore, there are 10 different connectors which you can quickly attach to the cable to plug into most anything. I believe that one of them is compatible with your AT power box gadget.

There are also a wide variety of accessories for using the mic for different applications.

There are also two headset microphones with the same interchangeable cables/connectors, etc.

I have a couple of the (1st generation) AT 899, which sounds good. The cables are rather stiff though.. Allegedly the later models have more flexible cables.
An OST mic yields the most bang-for-the-buck IMO. For around $200 USD, for a mic and a power supply / XLR adapter with the plug and jack. For instance a Sennheiser compatible mic could be used with a 100 series transmitter or in hard-wired config. The (Tram like) 801 and 802 have a presence peak. TL40 has a basically flat response.

I own two AT 899's and they are really pretty good for the price. I use phantom power so I don't use a AA battery, and actually sounds better WITHOUT a battery and connected to phantom.

My only beef is that the cable is really unnecessarily long.

Jonathan