I recommend either the:
1) poor-mans batery supply - $150
or
2) BPS - $425
As for the AC adapter, it is quite good. I guess if you cut the cable really short and reterminated with the plug, this might make it closer to the battery supply. Also, if you replace it with a linear supply at 12VDC, this would probably be an improvement.
Several customers have said that the BPS sounds even better if you disconnect all the power feeds to it.
The Turbo 2 has a good power supply in it compared to the orginal Off-Ramp Turbo, so the improved power supplies have a less dramatic improvement, but usually it's audible.
Steve N.