Rogue amps and PrimaLuna are also in your price range, and worth auditioning. I own a Modulus pre and used it for 10 years with a Classe CA-200 amp with Vandersteen 3 speakers. I would think Your system already leans to a fairly nice, laid-back sound. When I switched to a tube amp, my choice was the McIntosh MC275, which sounded darn good with the Vandies.
For more richness, you might look at Conrad Johnson gear. The MV-50/52 etc. for instance might be just the ticket for you, and save you some money too versus some of the other suggestions above. You need to be a little careful with the Audible Illusions, since it has relatively high output impedence. You should look for a power amp with higher input impedence. Also, you may be disappointed with the bass you get from your tube amp transition compared to the Classe. Everything's a trade-off, and you need to decide what matters most to you within the money you're willing to pay.
Enjoy the journey!