So what iperf is doing is really testing the maximum transfer speed (upload or download) of your network. You need a computer running iPerf in server mode (in my case the router), and then run clients at various computers to test the speed.
This is the results of running iPerf in one of the development machines.
Client connecting to 10.x.x.x, TCP port 5001
TCP window size: 325 KByte (default)
------------------------------------------------------------
[ 3] local 10.x.x.x port 42884 connected with 10.x.x.x port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.0 sec 1.15 GBytes 987 Mbits/sec
Next, I try this from my NAS.
[ 3] local 10.x.x.x port 33607 connected with 10.x.x.x port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.0 sec 1014 MBytes 851 Mbits/sec
And this is the throughput from my primary music player (running Snakeoil of course):
[ 3] local 10.x.x.x port 58196 connected with 10.x.x.x port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.0 sec 625 MBytes 524 Mbits/sec
Finally, I run this on the Raspberry Pi 3... And what an appaling result!!
[ 3] local 10.x.x.x port 35116 connected with 10.x.x.x port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.0 sec 338 MBytes 284 Mbits/sec
A quick google couldn't tell me anything conclusive. But it does appear network is a bottle neck with these Pis. As good as they are, there are restrictions when it's a SoC.
USB 2.0 max out at 480 Mbits/s anyway, so I reckon even at this speed the Pi should be able to handle high res or DSD relatively well. But there's not much room for error here.
ODroids, Banana Pis can sustain higher throughputs. They are also more expensive.
Anyway, why the new router? I am finally going to bite the bullet and seggerate everything in my network into it's own VLAN. Not entirely sure what that'd do, so watch this space.