Discovery Cables Plus Four vs Essence: Is there an audible difference?

Definitely a worthwhile difference. I've been using Essence and Essential for years. I also have the Plus Four that I now use for home theater. The Essence and Essential are great values...

Owned both and replaced +4 with Essence so I think there is a worthwhile difference, but it's not a large difference.  It's mostly at the frequency extremes -- deeper, tighter and smoother.  My systems were all fully balanced.

I've had Essence and Essential for several years now. It replaced Signature IC and 123 Speaker Cable. 
The upgrade was great but expensive as I bought new from Joe. 
Im driving a Simaudio Amp into Focal Sopra#2 speakers. 
The combination sounds sweet. 
I'm using balanced ICs now but the RCA sounded great too. 

I recently added a Plus 4 phono cable and I have some 12" lengths of Plus 4 inside my power amps connecting the input jacks to the first tube.  I have been very impressed with the sound of Plus 4 particularly the smooth, even tonal balance.  It has a very neutral sound.  It is hard to compare phono cables since I use a continuous run from cartridge clips to RCA plugs (the Discovery cable has a joint where the Plus 4 is connected to the tonearm wiring).  But in my power amps I have tried all sorts of connecting wires including Duelund silver ribbon and Neotech silver, and I like Plus 4 the best.

In years past I had an Essence interconnect and I have to say I was not as pleased with it.  It always seemed to add too much warmth and it was a little soft on leading edge transients.  I have never compared the Essence and Plus 4 head to head so I can't say for sure but I think the Plus 4 may actually have a more neutral tonal balance.