A headphone amplifier, with a low output impedance might help with a tighter bass. But as your doing audio production, you might invest into some Sony MDR-V6 monitor headphones (used $65?), they should(?) have less biased in the audio. As I would guess the Fostex TH900 MK2 headphone are more...

With 25-Ohm headphones, it's recommended to plug them into a headphone jack with an output impedance of 2.5-(Ohms, or less), for best damping control. Can't find a listing for the output impedance of the Motu M4, so it's output impedance might be well above 2.5-Ohms. OTL tube headphone...

Looks like the only digital output from the M-audio Fast Track Pro is coaxial. So you would need a DAC with S/PDIF coaxial input. But my two cents is to just get a newer Audio Interface. Budget?

Massdrop/Hifiman HD5XX headphones :)

I own the Essence STX (PCI-E), and used aftermarket op-amps. Stopped using it years ago and now stick to USB DACs. I've listened to modern $100 USB DACs and to me they sounded just as good as my STX. So something like a $150 Topping (E30 II) DAC should be pleasing to your ears :)

I would guess a modern $100 USB DAC would equal the Essence ST (PCI) sound card.

They are only 18-Ohms, so should not need much voltage to drive them. So my $25 FiiO battery powered portable headphone amplifier would drive them.

I own the DT880 600-Ohm, slightly bright sound, but other wise good sounding headphones :)

Are those 250-Ohm or 600-Ohm or other?

You mean single channel op-amps vs double channel op-amps? Each slot on the sound card is dual-channel, so it come stock with three dual-channel op-amps. Or you could use 6 single-channel op-amps, in those same three slots. I'm not the expert, but I believe single channel op-amps isolate each...

I've never listened to the Takstar HD6500, but I would expect the Takstar HF 580 (planar) headphones to sound better. (I own the Takstar HD6000 & HF 580). The Drop (Massdrop) Hifiman HD5XX are really good for their $180 price. https://drop.com/buy/drop-hifiman-he5xx

Which Takstar are you asking about? Check out the Takstar HF 580 planar headphones.

I own the HD58X, great for music, but my $179 Drop/Hifiman HD5XX are an improvement. https://drop.com/buy/drop-hifiman-he5xx

The HD58X are good music headphones, but not the best for detail. I like the detail of my Massdrop/Hifiman HD5XX headphones.

Put the DAC and headphone amplifier on separate surge protectors.

I've heard that the MDR-7506 is just slightly more brighter, than the MDR-V6. If you do buy a used MDR-V6, expect to spend an extra $10 for new (generic) ear pads. In the past 10 years, I've bought over 60 headphones (about half are lower costing "bargain" China stuff) and I'm fine with...

On Head-fi, it's usually recommended, for a given audio budget, to spend the biggest chuck on headphones, the amplifier gets a decent chuck of the budget, and the DAC gets whatever is leftover in the budget. The Drop (Massdrop)/Hifiman HD5XX headphones are a great bargin, I'm wearing mine right...

4-pin XLR female socket to 1/4" TRS adapter is sold on Amazon and eBay and AliExpress and other sellers. Try search for "1/4 TRS 6.35mm 4-pin XLR balanced female" should give results.

To me, audio production (assuming why you use the ID22) is better using boring sounding headphones, easier to analyze the sound. So not much voltage needed to using the HD6XX for boring sound. But for audio enjoyment, I would get a tube headphone amplifier, to bring out the 300-Ohm HD6XX to a...

Hifime optical DAC, $49 https://hifimediy.com/product/s1-spdif-optical-dac-es9018k2m/ Can we assume with the ID22, your using the 1L and R2 outputs for the speakers?

What model is the Topping HP amplifier. Amplifiers are normally analog, so why run an optical (digital) cable? The Audient iD22 already provides a DAC function.

SparkoS Labs Gemini has a very low output impedance .25-Ohms, so yea, good damping control for 38-Ohm headphones :) But spending $1000 for driving $300 headphones seems a little overkill.

The Grado SR325x are only 38-Ohm. You might look into hybrid (tube & solid state), which would have a low output impedance (Ohms)

I do not remember an negative issues with buying audio cables from Monoprice over the 9 years I have be dealing with Monoprice. But you could spend $18 (plus tax) on the three cables from BestBuy, cables that look very generic and un-shielded (in retail packaging). and if one is defective, you...

yea, connect the green, orange, black to the Sony's Multi Ch IN. I like Monoprice's price on cables, there generic no name cables. So when you order the 3.5mm TRS to dual RCA cables, you can order four or five, just incase one cable is defective. One has to wonder if the Logitech speakers and...