help me build a cheap second system

Since your accustomed with great transparency and dynamics(TAD) the ATC SCM-19v2 is your speaker. At $4300(retail) it does take up a huge chunk of the $7k limit. There are many used options to keep this around $7K, here are a few. 1-NAD 375BEE/565BEE, 2-Yamaha A-S2000/CD-S2000, 3-Denon DRA-CX3/DCD-CX3. The Denon set up is the most cost effective, is 75w/ch enough to drive the ATC? It's claimed it can drive a B&W 802 Diamond! With the NAD you have the most power and a great budget player. The Yamaha S2000 series would probably push you over the $7k budget but your getting refinement and build quality over the NAD gear. The Denon CX3 series is also very well made but the mid-size components might be a turn off. With cables I would look at Signal Cable-Silver Resolution. At 35lbs the SCM-19 needs a quality stand which you could find used. FWIW a used SCM-19(NOT v2) model could be had for < half the current model. But from everything I have heard(read) the new tweeter and cabinet justify the cost. Since ATC does not update very often you should have a current model for at least another 5 years.