Headphones volume not loud enough

[conticreative]

This is not a Mixcraft 8 issue at all, but I figured that maybe the kind members of this forum may have some tips for me.

I have a very powerful Win 10 workstation built for work that also makes for a dandy music recording machine. This is the third time in a couple of decades that I have setup a home recording studio and over the years I spent a lot of money buying expensive sound cards. This time around, I purchased a cheap Beheringer U-phoria UMC22 external sound card that actually works quite well for my needs. My much more expensive sound cards are now luxury doorstops for lack of modern drivers, so I decided to go cheap this time.

The problem I have is the headphone output of the U-phoria. The volume is terribly low (or that's what I thought). So much so that when recording acoustic instruments such as my guitar, the sound makes it hard to hear drums or a click track and keep time.

My headphones are old faithful AKG K240 that are at least 20 years old. I had to replace the pads, but otherwise when connected to a proper output, like my home stereo, they sound great.
Problem is that the U-phoria has a really wimpy output and the volume I get out of the headphone monitor is way too low. To fix that, I dusted off an old Alesis 8 USB mixer (AKA the "Buzz Machine") and discovered that as long as it is not connected via USB to my computer it works great as a mixer AND as a headphone amp. The buzzing only shows up when connected to USB and used as a sound card. Obviously, Alesis shoved a USB interface in the thing without redesigning some necessary circuit.

The problem is that now I have the equivalent of a boat anchor and a bunch of wires on my desk just to increase the headphones volume. It seems like overkill. The U-phoria has 2 audio ins (one mic/guitar and one guitar) and that's one more than I usually need, so having the mixer connected to it is purely so I can control the headphones volume.
Connecting to my studio speakers is a no go as I need to step down the plug with an adapter and the cable gets in the middle of everything. I tried. They sound great but I have had bad experiences with adapting large RCS males to small RCS females. A distracted pull and goodbye to my speaker's output jack.

Recently, I had to purchase a new set of Powered USB headphone from Amazon, having broken the USB plug on my expensive gaming USB headphones. They are Mpow headphones that come with a USB interface but also can be used as headphones for my iPhone, iPad, etc..
https://www.amazon.com/Mpow-Microphone- ... B06XWG12QS
They have a clever system where the USB interface is separate from the headphones proper. Even without the USB component they sound great on my iPhone, so I grabbed an adapter and connected it to the U-phoria headphone out.

The volume is perfect. In fact, I have to keep it at about 50% so I don't perforate my eardrums.

As far as I can tell, using the headphone part (sans USB) makes these passive headphones, so there is no reason why they would be so much louder than my AKG K240, but they are.
The problem is that they are cheap and using a converter to go from iPhone male plug to the larger headphone female jack, makes them prone to crackling and sometimes they don't connect so well.

I really would like to get my AKGs to be as loud without having to use the mixer.
After looking around Amazon, I found several headphone amps that would take a lot less space than the mixer, but the prices are ridiculous. They are more expensive than my U-phoria.

Could it be that my AKG K240 are shot? Or simply not designed to interface with more modern systems?

Should I buy new "prosumer" headphones with a proper male plug or should I invest in a headphone amp?

EDIT: I just realized that in looking at my AKG K240 on Amazon, the model for sale there are 50ohms. Mine are 600ohms. I have a vague recollection of how speakers and headphone work, but I think my answer is right there.
https://www.amazon.com/AKG-240-Semi-Ope ... dpSrc=srch

My guess is that there isn't a cheap way out of my dilemma. I'll have to purchase newer headphones designed to work with my equipment.

If any Audio Engineers are reading this and they know of a trick to make my AKGs volume to increase while plugged into the U-phoria, I'd be thrilled, but I have a feeling that I either have to buy new cans or get an expensive headphone amp.

EDIT2: Reading the specs of the AKG and a few links to other forums, I also realized why I have been plagued by the Mixcraft metronome getting recorded in my audio tracks (I had to change it to a bass drum to make it less noticeable). I thought it was due to spillage between tracks, but instead it sounds like the AKG are not insulating headphones, meaning the sound comes out of them and hits the microphone even at a distance, making my singing or acustic guitar recordings pick up the tic-tic-toc of the metronome.

I guess that's my answer right there. I am going to post this anyway in case someone else has the same issue(s) and they want to save some research time.

Thank you for reading.

[rsvette12]

This will make any headphones crank - little wonky but awesome and free

http://www.majorgeeks.com/files/details ... 4_bit.html

[Starship Krupa]

I realize that I am many months late on this, but headphone amps for this use are anything but "expensive."

Behold: https://www.sweetwater.com/store/detail/HA400

Behringer headphone amp, gives you 4 channels of headphone distribution for $25.