how to run three subs from one lfe jack

One possibility is subs that have a line out and you can daisy chain. Receiver outs go to first sub and out from that one to the next. Any amplitude loss can be compensated with sub volumes. 

If your receiver had a single sub output, it implies that it does not have the provision to do bass management of 3 subs.

Get a miniDSP 2x4 HD for the subs, if you care about the sound quality and more granular control. If the restaurant has 3 improperly setup pounding beasts, customers may jet quickly.

1. Not interested
2. In bass managementhe receiver will roll off thelows the subs are to fill out the freq response of small speakers as long as there’s some bass everyone is happy