so I was going for the Fostex ones because the older Denon models were using Fostex drivers

They were using fostex dynamic drivers, not planar drivers. Totally different.

It looks like you’ve done a lot of reading up but are misunderstanding a lot of things.

You’ll need an amp for those headphones, bass will sound better. If you want more bass then change the earpads. T50RP are very susceptible to this.

Just get an ifi dac. Those a good and have a little button for extra bass.