I like both the Spendor S3/5 and the Vienna Haydn. The Spendor is the more accurate of the two, revealing and analytically penetrating. The Haydn is the more euphonic. Based on your criteria noted, The Haydn is likely more satisfying to you than the objectively excellent Spendor.
However, more to the point of considering your request for
"...a speaker under $1500, decent bass response (flat to 60 hz), little cabinet resonance, somewhat laid back and a soft upper mid/lower treble response...."
A much closer choice is the Silverline SR16. For an even softer top end, the SR15 is voiced considerably warmer. Both of the Silverlines have better dynamic range, larger image and sound presence and deeper useful bass than any of the four you proposed.
Phil
However, more to the point of considering your request for
"...a speaker under $1500, decent bass response (flat to 60 hz), little cabinet resonance, somewhat laid back and a soft upper mid/lower treble response...."
A much closer choice is the Silverline SR16. For an even softer top end, the SR15 is voiced considerably warmer. Both of the Silverlines have better dynamic range, larger image and sound presence and deeper useful bass than any of the four you proposed.
Phil