Can "Dark"Sounding Speakers Be "Brightened"UP???

What you are describing is the difference between the soft dome in the Concertino and the ring tweeter in the Toy.  Cables won’t make any actual differences however like any placebo they can be effective if you believe in the change.  Changing amplification or using tone controls will alter the sound and may get them a little closer to what they are looking for.  In my experience tube amps can add a bit of realism to instruments like cymbals and that can liven up a soft dome tweeter.  It’s subtle so don’t expect it to shimmer quite like a ring or metal dome tweeter, but it should be a step in the right direction depending upon the amp/tubes.  My experience is with Dynaudio speakers (soft dome) and the Willsenton R8.  

Cables are the most expensive form of tone control.

Room acoustics and actual tone controls are usually far more cost effective solutions.

Having said this, if the user is fond of certain brands of cable like mid range Wireworld he may do much better going to more neutral wiring like Mogami.  A lot of big brand cables are, IMHO, deliberately darker, though they do seem to image a little better in exchange for that.

Starting at $149 you can buy a Schiit Loki Mini+ four band equalizer which will allow you to experiment with different settings to your heart's content. For $300, their Lokius expands this to a six band EQ. (They also have a still fancier unit for $1,500....)

I've always found it interesting that many audiophiles are so willing to adjust the tone quality of their system with wires, amps or preamps that offer only one change in the frequency balance of their system but won't consider a device that lets them quickly adjust the tone as needed by different recordings.

Just a thought....

@mlsstl , One should only spend as much on cables for max detail retrieval/preservation. Unfortunately, many dumb dudes spend on cables for tonal changes. Well...if every forum dude had enough noodle in his noggin to secure a engineering PhD, it would be an utopian society indeed. But, the stoopid tends to be larger in numbers always ( in comparison to the brighter ones). So, don’t bother....lol

@freediver Try the Benchmark stack on it, AHB2 amp | LA4 preamp | DAC3B dac. You can always try this on a home trial or take a chance and buy used.

With warm speakers this stack would open up the sound. Doesn't the Decco have a tube in it. Warm speakers with a tube is not my type of system.

A cheaper option is a Class D like the PeachTree GAN400. I am putting my up for sale on USAM.

Put a streamer into the path instead of going direct via USB from the laptop. Not so much for your issue but to improve everything in the sound.

I have not heard the Decco but owned the PeachTree Nova 150. That is terrible compared to the new Peachtree gear such as the GAN400 and better yet, the GAN1 (but should modded it by tweakaudio). I replaced $15K of gear wit the $1200 GAN1 + $600 mods. However, that unit can ONLY stream via SPDIF, no analogue sources allowed. I used ROON to both stream to that and control volume. I replaced my Benchmark stack with the GAN1 since it was similar for lower cost, though eventually the lack of analogue inputs made me sideline the GAN1 only for headphones.