I am saving up for a better preamp myself. An ARC with remote is my first choice, but it will take me a few months to scrape together the wherewithal. In the meantime, I got a very good bump in quality with a NuForce HAP-100 from Audio Advisor which I had purchased about a year ago. Volume control, four-source selection switch and a display on the front panel of this compact headphone amp/preamp. Sounds better than the old Lexicon I was using.
$400. I think Amazon may have a few left. Remote control, too. I've found it to be a good getcha-by preamp, and attribute its decent sound quality to the KISS school of design. No tone controls, no loudness, not even a balance. As soon as I connected it to the ST-Custom, I knew it was staying put until I make a move. Audio Advisor no longer has any, but they have similar preamps from Pro-Ject and Parasound. If you can find any of these used, so much the better.
I have owned preamps by NAD, Adcom, dynaco, and several assorted Japanese vintage brands/models that I found unimpressive. Other than running across a Nak CA-5 or -7 (maybe), a current budget model will sound good, and no need for recapping worries, etc. One of many ways to skin a cat.