Audio Systems: acoustics 4000, background music systems, infinity entra

Question
Brand is Acoustics.  Model is 4000.  They are about 28" X 12" x 12" with 4 speakers: (4-way) 12" hi-compliance woofer, 4" ferro-fluid cooled mid-range, 2 1/2" ferro-fluid cooled tweeter, 2" x 5" ultra-high freq piezo ceramic horn.  My center speaker is an Infinity Entra Center. The surrounds are Infinity also.  I have a JBL self-powered subwoofer.  The dinosaur's footsteps in Jurassic Park rock!  It seemed that when I had the speakers hooked up via RCA jacks the volume was not there.  An improvement was heard when I used the coaxial jack.  Was that cabling or receiver?  

So, what do you think?  Is a bigger receiver is in order?

Thank you for your prompt response.
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Followup To

Question -
I have a pair of speakers, Acoustics 4000, that I purchased 20 or so years ago which I have hooked up to my surround system, using them as front R & L.  I need to know if the 55 wpc (@5.1) onkyo receiver is enough power to drive them.  I have looked high and low for info to no avail.

Thank you.

Answer -
Hi Cathy,

  I'm betting that it won't be a problem, 85% of the time a modern receiver is WAY more powerful than anything you could get 20 years ago at a reasonable budget in the consumer market.   True, 55 Watts/channel isn't reall powerful, but if your speakers are even moderate sensitivity (say, 85dB @ 1w/M, which is pretty crummy), and they're sitting 15 feet from you, you're still going to get about 93 dB out of each. That's pretty darn loud for a very conservative estimate.
(I typically design background music systems to output 75-83dB, 93dB is more than twice as loud).  
If your speakers are more efficient or closer than my guesses, then you'll definately be able to output more than you need.
If not, or if you already feel like you're not getting the "Oomph" you expect, you may want to consider something with a bit more power - I'd speculate that 100 Watts would do the trick.

  However, your description of your speakers doesn't ring any bells so I can't say for sure...
Can you give me more information?  
Is "Acoustics 4000" the brand, or model of speaker (or both)?  
How big are they (rough estimate is fine) and how many speakers are in the loudspeaker box?

  Also, what are you using for your "center channel"?  I think it's great when people can enlist their favorite speakers of yester-year into a new surround system, but it can often be difficult to find (or manipulate) a center-channel to match.

Answer
Got it...

I'm betting it sounds pretty good.  55 Watts is probbly fine for those speakers in your home environment  Alot of old 4-ways were voiced to get the most out of 25Watt-50Watt stereo amps even if they were rated for 150W or more.  Ultimately, it's all about practice over theory - if you're happy with results who the hell am I to pull some numbers out of the air, do a calculation, and tell you you're wrong.

The increase in "volume" probably has nothing to do with the cabling you've used and everything to do with the improvement in signal loss/attenuation and the increased signal:noise ratio you experienced by going direct from your source deck to your decoder in the digital realm.  Take that as a good sign.

I often wrestle with finding a good center-channel match to these massive vintage speakers.  With a 4-way combining a cone low-mid dome high-mid and hron-loaded tweeter I'd be hardpressed to recommend anything - B&W and Klipsch still have a few boxes voiced like the old days but Klipsch typically drives their horns much lower than yours is and I doubt it would mate well with your cone/dome mid section.  Officially, I say that if you're happy with what you have don't go changing it.

I wish you luck, enjoy!

One last follow-up question:
Can I come over to watch Jurrassic Park?