Voicemail, old pbx, dahdi lines

Old Voicemail4000 box is connected to the Toshiba Strata DK 280, and is going to be replaced with FreePBX box.
The new asterisk box has 4 ports FXO PCIe Card TDM410-40 installed.
Between strata and freePbx are 4 rj11 analog lines.
The old voicemail box answers the call, plays the message and asks for the extension.
PSTN call is switched to the extension entered by the caller.

PSTN----Strata PBX—freePBX

Current Situation:
Outside call from PSTN is goes through strata, answered by the asterisk, and greeting message is played.
Now I can switch the incoming call to the voip extension on freePBX.
But how to switch the call back to the strataPBX in order to enter strataPBX user extension?
How to make Strata answering request to go to desired extension?
I tried
1.) Extension number that is built into the DAHDI channel module *72andext, but it does not do anything.
2.) inbound route catching any call, switch incoming call to configured outbound connection back to the strata pbx and enter extension
No luck… Looks like the call is trapped on asterisk box.

What should I configure to enable outside caller to be switched out of the freepbx voicemail, and enter strata pbx extension?
What is the right way to do it?
Thanks in advance for any help.

Could DISA or flash cmd be used for that purpose?