I owned the X-250 and X-1 preamp and they worked really well together. I also came to realize that the X-1 was a really good preamp versus a bunch of others that I tired. I also found that the X-250 worked well with any active preamp I tried tube or SS. The best preamp that I mated to the X-250 was the Tom Evans Vibe. That preamp was something very special. There were a few tube preamps that really added that nice tueb mid range to the X-250 such as the Blue Circle B-3 MKII and older Counterpoint SA-5s & 5000s. I also did not find a really big difference between RCA or XLR cables, the XLR offering a quieter background and slightly better clarity and details but not worth changing all of you cables for.
Happy Listening.
Happy Listening.