I personally have never heard anything negative said about Audio-GD, when it comes to shipping.Could be one person is in charge of the shipping stuff and has not got around to sending the tracking number to the customers.
I'm going to guess(?) your Denon receiver makes a decent enough headphone amplifier, for driving the 300-Ohm HD650.
With the Shure SRH-1840, i would think buying a low impedance headphone amplifier, would be needed (which might also improve the SR325i audio quality).
Can't really find a lot of detail on the Lenovo y50's audio.It does use RealteK audio (chip and drivers), so how good the headphone surround sound is, i can not say, hopefully you have updated to the latest audio drivers/software.I know zero about the SkullCandy SLYR, but it looks like it works with gaming consoles.
I really do not know a lot about the G4ME, but my two cents is I do not think you will get much, if any improvement, getting the HD598 or G4ME, over the HD558.I would think (assume) your current HD558 sounds almost exactly like the HD598.I would say to invest into a Creative Labs Sound Blaster Z sound card ($90-$105), I would assume it would offer an improvement, over on-board audio.What is the make and model of your motherboard?
The HD558 and HD598 use the same 50-Ohm drivers.
Have you removed the black rubber tape from inside the cups of the HD558s.
The black rubber tape covers about 40% of the air holes, so removing the tape makes the HD558s more open.
What sources are you plugging the HD558s into (DAC/Amp)?
Here is a aftermarket cable (1.2m to 3m) for the HD558/HD598 that comes with a 3.5mm...
I would not buy the Amazon UK listing, as it sells the exact same set of pads for the AKG and Beyers.The AKG (and Samson & Superlux) use a slightly larger ear pad then the Beyer (DT770/DT880/DT990). I bought my AKG K240 Velour ear pads from Thomann, I use them with my Samson SR850 and AKG K240M Monitor (600-ohm) headphones.I ordered stuff in bulk from Thomann (UK) and had it shipped to California, so my total cost per pair of velours was $25 (18.3 Euros), normal USA price...