I am doing the same, using both of my powerflarm ports.
Powerflarm can certainly support multiple displays, in fact it also drives my XCSoar, so a total of 3 devices connected to it.
As for antenna position as other recommendations and tips, flarm provided detail recommendations, the problem is that it requires investing time to research or money for a professional installation. Since most of us install ourselves and don’t utilize the B antenna, the results vary significantly. But I found out that most installation are adequate for most situations.

Ramy

On Friday, June 4, 2021 at 12:32:12 PM UTC-7, wrote:
On Friday, June 4, 2021 at 9:49:52 AM UTC-5, wrote:
I could not feed Flarm information to both the Butterfly Vario and the LX 9070. Flarm kept losing the configure. Richard disconnected my Butterfly from the Flarm and problem solved. I am wondering how I could you have both Butterfly and LX operational with Flarm at the same time? Thanks in advance.
On Thursday, June 3, 2021 at 10:10:25 AM UTC-7, Ramy wrote:
Roy,

Even with carbon blocking there should have been an alarm. The carbon reduces range but should not completely block. If this was the reason this is a strong case for installing B antenna in the belly. It would have been worthwhile to send both igc files from each powerflarm to flarm team to analyze, as it includes log data for all other flarms it receives. It could be a flarm display configuration issue. Unfortunately there is no standard nor best practice as of how to configure your display effectively. Every one configures differently, and some just keep factory defaults which are often wrong. I have both my old butterfly display and my LX9000 and the butterfly display provides more warnings than my LX9000. It should be fixed in the next LX Firmware release.

Ramy
On Thursday, June 3, 2021 at 9:54:58 AM UTC-7, Roy B. wrote:
Further to the continued need for old fashioned "mark one eyeball" is recognition that Flarm does not work in all geometrical situations.
I was an unwitting participant in a comp near miss where 2 gliders (both with correctly configured, non stealth set Flarms) failed to detect an imminent collision with the two gliders approaching each other 45 degrees off of head on and one slightly higher than the other. It was over in a matter of seconds, and fortunately we saw each other at the last moment, he pulled and I pushed, and he passed close over me. Neither of our Flarms gave any warning. In our talk about it afterwards we theorized that the carbon underbelly of the higher glider blocked the transmissions between the two Flarm antennas (both of which were mounted on our glare shields). Both Flarms continued to work properly throughout the competition.
ROY
I don't have a LX but I do feed my FLARM data to both a Butterfly display and an xcsoar based flight computer display and it works perfectly. I use the FLARM RJ-45 output to go to the Butterfly display and I use the FLARM DB9 output to go to the computer. Are you trying to drive both devices from just one of the FLARM outputs in a daisy chain fashion? Another thought is to check the various protocols you're using to send data to your devices. In my case I have both FLARM data channels running at 57k bps. Your Butterfly display should automatically discover and configure itself for the proper data rate so no reason to use anything less than the maximum speed. I have the RJ45 channel (output 1) sending FLARM and GPS data in default format and the DB9 channel (output 2) sending just FLARM data in format 7 (My computer gets its GPS data from a 302 vario). The FLARM config statements that set all of that up a
$PFLAC,S,NMEAOUT2,73
$PFLAC,S,BAUD2,5
$PFLAC,S,NMEAOUT1,1
$PFLAC,S,BAUD1,5

Robert