New member here so go easy.

I stumbled across AoS months ago whilst looking for potential upgrades for my Beresford Bushmaster mk1. Thinking this is the place to go for the advice I'm currently seeking.

My current system comprises of:

Synology DS212j NAS -> 3rd Gen i5 PC (SSD, 8GB RAM, AMD R9-290 GPU, Gigabyte motherboard) with coax out -> Bushmaster mk1 (with firmware upgrade and linear power supply) -> AKG K701.

I love the sound of the K701's with the Bushmaster. Some badly recorded/mixed tracks can sometimes sound a little bright but not often at the volume levels I listen at. The rest is fantastic. Just about enough well controlled, tight bass, fantastic airiness and soundstage, beautiful mids etc. However, lately I've been wanting a little more. So my first path was to start looking at some shiny new cans, however, before I drop £600 or so I thought it best to seek advice especially as I like the K701's so much.

So my question is - Am I getting the best out of them currently?

Starting with the NAS drive. Is this a good music server? NAS drive connected to the LAN with CAT6 cable. Into PC using same CAT6 cable. I know a little about computer hardware but is there any scope for errors in data transfer and retrieval here?

Next the coax out on the PC. This is directly off the headers on the Gigbyte Z77D-P3 motherboard. Is this the best method to get the digital information out to the DAC? I have read that a soundcard should be better as it connects to the PCI lanes which provide a better (less prone to jitter) output.

Playback software. I started using Foobar2000 recently to try ASIO as I understand Windows by default resamples everything to 48khz as taints the sound and ASIO gets round this problem. However as of now I can't get ASIO working with my digital out. But again, am I barking up the wrong tree here?

And then the Bushmaster. I bought it over 10 years ago to use with a Logitech Squeezebox system (and various other items at the time). She's had a firmware upgrade a couple of years ago along with a Chinese PSU upgrade recommended by Stan, but are there any other upgrades that can be done? do Stan's new models offer more than the Bushmaster both as a DAC and headphone amp?

Don't get me wrong here, I'd love some shiny new headphones but...... I'd like to optimise the rest of the system first.