To me the specs on the X250.5 do not look like a match for any type of passive (low sensitivity, input impedance, and gain). A low output impedance active preamp should do the trick, or the Pass B1 buffer preamp.
Many fine active preamp recommendations above. If it were me I'd stay in the Pass family, but the Klyne's have always been intriguing. I also own a Rowland Capri and while it is a lot of preamp for the money, especially at used prices, I can't say how it might match up with the X250.5.
Many fine active preamp recommendations above. If it were me I'd stay in the Pass family, but the Klyne's have always been intriguing. I also own a Rowland Capri and while it is a lot of preamp for the money, especially at used prices, I can't say how it might match up with the X250.5.