After a lot of futile consideration, I ordered a Practical devices XM-5. I have a Microshar 107B that drives my AKG K240S pretty well, but, like you, I wanted a DAC to use with my laptop.
The Ibasso BOA is priced better, but the opamps are soldered in, and I have had little success looking for the Viper w/ sockets. PD included a sample AD8397 op-amp, and swapped the cable for the charger/battery, so I went for it. It has a lot of features that others don't have...many I'll probably not use. AND... they have a 30 day trial period
