+$200 maximum for dubious improvements.
Seems like a lot more than dubious improvements to me:
From the latest post on the RME forums:
"
Differences ADI-2 Pro to ADI-2/4 Pro - Brief Overview
Extended and improved RefLevel structure: +1 dBu, +7 dBu, +13 dBu, +19 dBu, +24 dBu
Same RefLevels on Phones Outputs as 3 power states: IEM (+1 dBu), Low Power (+7 dBu), High Power (+19 dBu)
Independent RefLevels for Line Out 1/2 and Phones Out 1/2
Phones Output Power raised to 2.1 W unbalanced and 3.4 Watt balanced, 32 Ohm
New True Balanced Phones output scheme
Therefore Balanced Phones output independent from Line Out 1/2, full use at the same time
Added menu page for configuration of Phones 1/2
Dual Volume control now also available in balanced phones mode
Pentaconn connector for ease of use
Input impedance unbalanced raised to 45k - > compatible to Moving Magnet cartridges
Input impedance balanced raised to 90k - > ideal for measurements
Improved input stage, no added distortion even at lowest RefLevel that needs amplification
ADC: Selected ES9822Pro for lowest THD, highest THD+N and SNR
AD measurement bandwidth flat up to 200 kHz
AD filters selectable even at 384 kHz sample rate
DA frequency response expanded from 110 kHz to 350 kHz
DA filters selectable even at 768 kHz sample rate
De-Emphasis available even with NOS selected
New output stage delivers full SNR even at low RefLevel +1 dBu
Rear TRS outputs can be switched from 1/2 to 3/4
Trigger Out to control power amps etc
Full MM cartridge support: RIAA EQ and various gains included
Special feature Bass Mono to reduce rumble and groove noise
Comes with new, semi-grounded 40 Watts SMPS with IEC socket
And 114 page printed manual"