USB Powered DAC dilema

Hello guys,

I have a chinese DAC based on XMOS U8, AK4490 DAC and NE5532 OP-AMP ( now OPA2134). The board should be externally powered by a 9V DC and the power route is like this:
9V->L7805->AMS1117 3.3V -> XMOS, Atmel chip, cloks
9V->L7805->DAC 5V pins -> AMS1117 3.3V -> DAC 3.3V pins
9V-> some filters -> Op-Amp - this is a guess because the board is multilayer and I can't trace the whole circuit, but on the +Vcc pin I have something like 8.5 V

I want to transform the DAC to be USB powered ( I know, a heresy), but I don't know what route to chose without breaking the bank(if needed) but still preserve a nice sound.
My findings until now are:
-the 5V from the USB is only used to power a LED
-the total power consumtion of the board is 160mA
-bypassing the 7805 reg and feeding directly 5V from the USB is working but the sound is very distorsed at higher volume - I suspect because the voltage on the Op-Amp is only 4.4V
-by using a lab power source I powered the board and I didn't hear any difference between 7 V(minum drop for the L7805) and 9V(the maximum that I would use for the 7805 to drop)
-in my local electronic shop I have found DC/DC 5V to 5V 3W isolated converter, isolated DC/DC 5V to 9V at decent price with 222mA(2W) otput current and very very expensive with 666mAh(6W) - nothing in between power wise and all switching at 100kHz
My options are:
1) use the 9V 2W DC/DC converted and ADUM4160 to fully isolate the USB, then some pasive filters followed by a good LDO to suply ~7-8V to the 7805's and Op-Amp
2) use the 5V DC/DC converter and ADUM4160, some filters and change the power route for the Op-Amp to get the minimum 5V
3) build a boost converted to reach 9V but with a much higher switching freq ~1M and more current output, and then the same: pasive filters followed by a good LDO to suply ~7-8V to the 7805's and Op-Amp
My concerns are:
-for method 1 the power consumtion is near the max power for the DC/DC converter
-for method 2 the Op-Amp will not get any LDO
-the DC/DC converter are working at low freq
-the method 3 is not galvanic isolated from the USB, but I saw that other good spec DACs like Khadas Tone 1 are also not galvanic isolated

What do you guys think? I am also opened to other sugestions.
This is the board, it has some changes on it because I am testing different power configurations.
 

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ok, so you all are saying that I should drop the DC converter and use straith 5V from the USB with apropiate filtering + low supply voltage op-amps. This will work, but my only consern remains that the DAC will have a non regulated 5V to use it as VrefHL. How could I fix this?
 
This will work, but my only consern remains that the DAC will have a non regulated 5V to use it as VrefHL. How could I fix this?
You could use slightly lower VDDL/R & VREFHL/R. E.g. LP5907 has 4.5V output version or TPS7A94 which has adjustable output with only 150mV dropout.

Of course option 3 is ok as well but more complicated unless you use some prefabricated device. No need for an LDO between boost converter and L7805.