Just to add to the Thiel discussion, I use 1.6s and a SCS4 for a center and am very happy with them. You can certainly do that on your budget, although the speakers can be hard to find used. My one caution would be that the Pioneer may be somewhat bright with the Thiel speakers. IMO Pioneer can be bright, but I do not know if that is in the pre-pro or amp section of their receivers.
Just looked, a pair of 2.4s and a MSC1 are up for sale for $2750 but that would not allow a new pre. You should note that the MSC1 is a big speaker. That is one reason I went with the SCS4.
You might consider getting a used receiver that has pre-outs. Since receivers are high volume compared to 7.1 channel pre-pros using a receiver and ignoring the power section is often a good compromise. Sounds like you may already be doing that with the Pioneer. A used NAD or Marantz might be a good option since you are interested in 2 channel. The lower end NADs do not have room correction and have fewer options than most receivers, but I like the 2 channel sound. You could probably get a used 775 which does have room correction. A Marantz like the SR7007 will have room correction. If you are interested in NAD look at Spearit Sound. They are an authorized dealer and have used and refurbished equipment.
Just looked, a pair of 2.4s and a MSC1 are up for sale for $2750 but that would not allow a new pre. You should note that the MSC1 is a big speaker. That is one reason I went with the SCS4.
You might consider getting a used receiver that has pre-outs. Since receivers are high volume compared to 7.1 channel pre-pros using a receiver and ignoring the power section is often a good compromise. Sounds like you may already be doing that with the Pioneer. A used NAD or Marantz might be a good option since you are interested in 2 channel. The lower end NADs do not have room correction and have fewer options than most receivers, but I like the 2 channel sound. You could probably get a used 775 which does have room correction. A Marantz like the SR7007 will have room correction. If you are interested in NAD look at Spearit Sound. They are an authorized dealer and have used and refurbished equipment.