Hmmm... bargain DACs.
First, I've got to comment on the Grant and the Lampy..... I don't at all hold with "tube DACs". Since a DAC is basically a solid state device, the only possible reason for adding a tube would be to add tube distortion. (You may have twigged that I'm not a tube fan.) You haven't avoided anything solid state, or eliminated any hard that solid state parts might cause, all you've done is slathered tube distortion on top of it. While I'm personally not a fan of tubes, I do understand those who are. It seems to me, though, that the tubes belong in a preamp - or a headphone amp - and not in the DAC. It just seems like a silly place to put them.
Now, as for "bargain DACs", there are a lot of good deals out there and, quite honestly, plenty of cheap DACs that sound pretty good. Since this thread is about "Frugal DACs", we should start at the bottom.
Fiio makes a few DACs in the $40 range that, amazingly enough, fail to suck all that badly (check Amazon).
Someone else mentioned the little Turtle Beach one (at $25).
Any of those would be a HUGE improvement over the sound card in a laptop - even an expensive laptop.
Going up, there's the HRT Headstreamer for $135 (it's a USB powered headphone amp, and uses the better asynch protocol). You can also, of course, plug in an adapter cable and connect it to a real system (a pretty good alternative if you want a headphone amp AND a cheap DAC.) It sounds quite nice, but is USB only.
HRT makes other nice little "black box" DACs, but the Headstreamer is more universally useful.
I really wanted to love the DragonFly, but I can't. The build quality is lovely (it's solid metal with that rubbery feeling coating), and I love the kewl color changing logo for sample rate, but it is rather pricey at $250. As a buddy of mine commented "the sound won't offend anybody, and it sounds nice, but it just doesn't sound exciting". I would say the Headstreamer, at almost half the price, sounds a tiny bit better. The DragonFly is much smaller, which is nice, but having a USB dongle with a headphone cable hanging off its butt is definitely asking for that USB connector to get loose in a few weeks or months and, if you add the extra cable, then it isn't nearly as tiny.
The Emotiva XDA-1 sounded VERY nice - especially at the $150 clearance price, but it's gone (if you see one cheap on eBay, grab it, and don't forget to transfer the warranty). Some of us thought it actually sounded a bit better than the Benchmark. Emotiva has a new one, the XDA-2, on the way in a few weeks. It's a bit more expensive, but has a lot more features (including an ASRC and a really nice headphone amp), and comes with a 30 day return option. (Full disclosure here; I work for Emotiva.)
The Schiit Bifrost is very nice (it's what I currently listen to at home). It also includes the better asynch USB and all around sounds very nice. The Gungnir is probably nice as well, although I don't see the ability to lock onto non-standard clocks as terribly useful (most sources aren't nearly far off enough to need it.)
Up the chain, the Benchmarks are still very nice, but there are just too many cheaper alternatives out there now that top or equal it.
(Especially, the premiums they charge for an analog input and a remote volume control are a bit excessive.)
Folks like Audio-GD make a whole slew of DACs, and some of them I know sound nice, but they're a bit "all over the map" in terms of sound....
(I have one of their $200 DAC/headphone amps and it's quite nice).
Personally, I would avoid models that make you go inside and change jumpers to change sample rate or filter options -
you end up NOT trying the alternatives because it takes too long and is too much trouble. Go for one with SWITCHES.
There are a lot of other "no-name" Chinese DACs on eBay and elsewhere. Many sound quite good, but not all, so be very careful about buying one
based only on claims - without either listening to one or at least talking to someone who has.
(Remember, not everything with a Sabre, or whatever, actually sounds good.)
Finally, don't discount the benefits of a really good USB-to-S/PDIF converter.
I had an old V-Link, and it definitely made an improvement to my Emotiva XDA-1, and the Audiophilleo 2 was an obvious improvement on that...
I use the AP with my Bifrost and it makes a huge difference (but, then, it cost as much as the Bifrost) so there IS something to reducing jitter to really low numbers....
I would also warn that expensive DACs, say above the $1500 price point, get somewhat "subjective".
I heard a $30,000 one once.... it didn't sound any better than the $1000 one sitting next to it...
Don't assume... and listen carefully.
Oh, and, yes, if you get a DAC with an asynch USB input (like the Bifrost) or a converter (like the HiFace, or V-Link, or Audiophilleo),
then you should expect any differences you might hear between USB cables to be minimal (or nonexistent).
(From an engineering point of view, expectations should tend towards nonexistent.)
If you have a NON-asynch USB input, then who knows?
DO try for a double blind test before spending the money, though....
DACMan