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

@mashif is correct. Just get subs you can daisy chain.

Can't need to use a particular su and daisy chaining may not wok logistically 

You can put a couple of these together and create more outputs from the receiver.

https://www.transparentcable.com/products/rca-y

No you cant you need an amplified splitter 

How about purchasing three wireless subwoofers, and running them off a wireless sub transmitter? No long RCA cable runs needed. 

Who told you about needing an amplified splitter? Your receiver is your line level amplifier. You adjust volume on the subs. The only real issue is noise due to cable length but 20ft isn't bad unless it's a very noisy electrical environment. 

You can't split an rca output  threetimes and run 60 plus feet of rca cable

Yes you can. 

One sub from the receiver

Two subs from 2 speakers  

https://www.residentialsystems.com/technology/audio/svs-debuts-soundpath-speaker-level-subwoofer-adapter

I am sure there is something in the pro world for running powered speakers that would work. Maybe call sweet water and ask them.

Some active crossovers will let you run 3 subs with active gain output (preamp). Sublime acoustics is a good example. Two subs could run off the RCA outs and one off the XLR as both are active at the same time.

For background music I would just use a Y adaptor or two and turn up the receivers sub gain 90% and then adjust it down in the subs as needed. 

Audiotroy call audiokinesis.

Rolls DA134 Line distribution amplifier

SPECIFICATIONS
The DA134 is a four channel RCA distribution amplifier with RCA and
1/8” inputs that can be switched from mono or stereo. The DA134
Distribution Amplifier will distribute a mono signal to eight outputs,
or a stereo signal to four stereo outputs. The outputs are designed to
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Input Impedance: 10 KΩ
Max Input Level: +12 dBV
Output Impedance: 470 Ω
Max Output Level: +12 dB
Max Gain: 20 dB
S/N Ratio: >90 dB
Cross Talk: -70 dB (stereo)
Frequency Response: DC - 60 kHz, +/- 1 dB
THD: <.008%
Power: 15 VDC
Size: 6.5” x 3.5” x 1.5”