I agree with Todd, and not only because I run virtually the same rig. There really aren't any 24 bit A/D converters that are small and portable except for something like the Mytek, which may be overkill. At first, I was suspicious of the A/D on the D50, given the fact that their portable onboard DAT A/D converters were terrible. I really like how the D50 sounds however, so Sony finally got it right, IMO.
Does the 148 have a 1/8" output? I haven't had any problems with going 1/8" > 1/8" on my PSP-2 > D50 and it sounds fine. If not, could you go XLR ? 1/8"? While it may not seem secure and appear chintzy, in practice, the 1/8" input for the portable devices actually works well.
Bottom line, I would consider the Sony D50 or the Marantz 661 if you are trying to keep the rig to a reasonable size and with good quality. When I was making this decision, I also looked at the Sound Devices machines and judged their onboard preamps to be total crap. All of these units have good quality A/D converters, however, so I would recommend running one for a little while and seeing how it sounds before investing in a Mytek or something like that.