Seems to be nearly identical to the AST Advantage! Pro 486SX, with merely a different front bezel and drive bay arrangement:
This one isn't mine -- borrowed the image from RetroSteamTech's blog. Mine is still the "before" picture, heavily yellowed and with a crack under the 3.5" floppy bay.
I have the SX/25 model. When it boots up, the BIOS even IDs itself as "LC". 😀
I have found very little online about the Advantage series. The Bravo line seems more prolific. But you're right, they are a bit anemic. This is a re-buy of my first PC, although my original was a notch down -- SX/25 with 85MB WD Caviar HDD and 2MB RAM. I bought it new for $999. The one I have now is similar to your config -- 170MB WD Caviar HDD, 4MB RAM, Cirrus 5428 video. No stock sound card or CD-ROM, though.
I have added a PAS16, since back in the day I had used my dad's hand-me-down SB Pro 2.0 until I got the Media Vision Pro Audio Studio 16 for Christmas. Never had a CD-ROM in this PC. The previous owner of my new one had added an SB16 and Goldstar 8x IDE CD-ROM, which I took out and used elsewhere. It also came with a modem. I left that in (for no good reason except that it appeared to be original) and added a 3Com 3C509.
I've also added another 4MB stick of RAM for a total of 8MB. For a brief moment, I had installed an additional 16MB stick for a total of 24MB. It passed Memtest86 just fine, but it took a little longer to boot counting all that RAM, and frankly, it just doesn't need that much.
I hope you already have that 540MB drive. 😉 I tried a 720... 750.. 7-hundred-something MB, but the BIOS is capped at 1024x16x63 CHS. It works (limited to the BIOS cap), but I hate to waste the extra capacity, so I just picked up a Caviar 2420 (425MB) which arrived today -- even has an AST part number on a sticker. 😀 I would've liked to have the extra 120MB of a 540MB drive, but the retro community is quite determined to hit that CHS ceiling, so they're always way more rare and expensive than their 420MB equivalents. I'll make do.
There's an OEM version of DOS 5 for these (see WinWorld for information about this on their DOS page), which interestingly, seems to be MS-DOS with IBM-style naming convention for the kernel files. IIRC, mine shipped with stock Windows 3.1 disks, MS Works 3.0, and an "AST VGA Drivers and Confidence Test" floppy. I found an image of the latter, but it's not the correct one for my model. The drivers look to be for a Paradise VGA chipset, I think, and do not support 1MB video RAM based on the resolutions available in the OEMSETUP.INF file. The confidence test works fine, though. (If anyone has an image for this disk that has Cirrus drivers, I would love to know! In the meantime, I'll use generics and hope I run across my original disk some day.)
Mine shipped with the mouse in the image above -- a Logitech re-brand -- and an AT keyboard be SEJIN, similar to this:
The only difference being, mine has a dark gray overlay around the LEDs and printed AST logo on the top left corner above the Esc key. I just took mine apart and gave it a thorough cleaning -- looks good as new. I don't have a picture of it, though -- hence the Ebay image rip. I played with this PC a bit last weekend and it is an absolute joy to use. It's whisper quiet, and typing on that keyboard feels like catching up with an old friend.