Other secondary sources have the Eva Maria Magdalena KAPP who married Joh. Georg DIEFFENBACH as the daughter of Joh. Geo. Martin KAPP & Eva Margaretha GRAFF.  Without primary documentation, I can't tell which is correct. 

1.  F. Edward Wright.  1994.  Berks County Church Records of the 18th Century.  Vol. 4.  Family Line Publ., Westminster, MD (Broderbund CD-166).

SELECTED PASTORAL RECORDS OF JOHN CASPER STOEVER of baptisms and marriages performed in the general area of Berks County... Tulpehocken - Marriages... 1739... December 8 - Andreas Kapp and Regina Sophia Siegmann.

Johann Friedrich KAPP and George Veitt KAPP are on the same list.  John Casper STOEVER was Evangelical Lutheran; church was near Bernville, PA. 

2.  Ralph Beaver Strassburger (William John Hinke, ed.).  1934. Pennsylvania German Pioneers: a Publication of the Original Lists of Arrivals in the Port of Philadelphia from 1727 to 1808.  2 vols.  Norristown, PA (reprinted 1966ff by Genealogical Publ. Co., Baltimore, MD; Broderbund CD-267).  From Volume I:

p. 86	[List 23 C] Palatines imported in the Ship Adventure, Robt Curson, Mr from Rottr. Qualified Sepr 23d 1732...
p. 87	Andreas (X) Kap... September 23d 1732. At the Courthouse before the Governor & sundry Magistrates the foregoing Qualifications were taken & subscribed by the several foreigners whose Names are contained in this & the preceding Page. Robt Charles, Cl. Con.

3.  Israel Daniel Rupp.  1876.  Thirty Thousand Names of German, Swiss, Dutch, French, and Other Immigrants in Pennsylvania from 1727 to 1776.  (repub. 1931, Leipzig; republ. 1965, Genealogical Publ. Co., Baltimore, MD; Broderbund CD-267):

p. 465	APPENDIX No. XIV. NAMES OF EARLY SETTLERS IN TULPEHOCKEN, BERKS AND LEBANON COUNTIES. — As early as 1723, thirty-three families of Germans, who had come to New York 1710, settled in Schoharie 1713, left there and located on Tulpehocken Creek; among these were... In 1728, others from Schoharie settled here... Andreas Kapp...
p. 466	The first settlers in Tulpehocken were Lutherans and German Reformed.  Rev. Tobias Wagner was the first pastor of the Lutheran Congregation.  The following is a List of the members of the Tulpehocken Church, from 1743 to 1746: Friederick Kapp, Andreas Kapp...
p. 467	Joh. Martin Cass, Geo. Vitus Cass, Joh. Michel Kapp...

"Cass" is obviously a misreading of "Cap."  The five KAPPs in Tulpehocken are considered to be brothers.  The big question is: who is the Andreas KAPP who came through New York?  Some say (see MacKenzie, 1907, below) the Andrew in NY is our subject, but if so, we are wrong about our subject's age and parents.

4.  Messages in the Copp Family Genealogy Forum (online at GenForum.com), including:

The baptismal entry in Christ Lutheran Church (Tupelhocken) Berks Co. PA 9 July 1744, 13th Sun after Trinity Christian, son of Joh. Andreas Kapp et UX Sophia Regina, n. Mullerin. child sponsored by Christian Muller.

Records of Christ Lutheran Church (Tulpehocken), Berks Co., PA Christian, son of Andreas KAPP, confirmed on Palm Sunday, 1758, at the age of 13 yrs and 9 months.

("Müllerin" is the feminized form of Müller.)

5.  Lyman Chalkley.  1912.  Chronicles of the Scots-Irish Settlement in Virginia: Extracted from the Original Court Records of Augusta County, 1745-1800.  3 vols.  Commonwealth Printing Co., Rosslyn, VA (reprinted 1965, Genealogical Publ. Co., Baltimore, MD; online in the USGenWeb Archives):

p. 221

Tipton vs. Werner--O. S. 302; N. S. 108--Copy of record from Shenandoah.  Bill filed 1804 by John Tipton. Defendants are, viz: Henry Keller,

p. 222

Michael Copp, administrators of Philip Werner; Barbara Werner, widow of Philip, and Philip's children, viz: Philip, Sophia, Elizabeth, Catharine, Peter, Sarah.  Philip was in 1796 resident in Berks County, Penna.  Deed, 25th August, 1797, by Jonathan Clarke, Philip Williams and Andrew McKay, Commissioners to John Tipton.  Sale under Act of Assembly, 4th December, 1795, to sell certain lands of Jost Hite, Robert Green, William Duff and Robert McKay, 400 acres on Tom's Brook adjoining Augustine Borden, Jacob Keller et al.  Recorded in Shenandoah, 12th December, 1797. Deed, 12th September, 1797, by John Tipton and wife Elizabeth to Werner's heirs.  Recorded.

Philip WERNER appears to be the son of Regina Sophia MÜLLER, by her third marriage, to Peter WERNER.  Michael COPP is likely Regina's son by her second marriage, to Andreas KAPP.

.  F. Edward Wright.  1996.  Abstracts of Berks Co., PA, Wills, 1785-1800.  Family Line Publ., Westminster, MD (Broderbund CD-209):  On p. 1041:

Pennsylvania Wills, 1682-1834 WERNER, PETER, Heidelberg. May 30, 1786 - July 3, 1786. Devises his farm to son Philip for £150. To dau. Magdalena .... Directs that the money for which he sent Conrad GROSS to Germany with a power of attorney shall be divided equally between his 2 children. Bequeaths to Rev. SCHULTZ £10 towards building a new Lutheran church in Tulpehocken. Exrs: John ECKERT and son Philip. Wits: Frederick KAPP and George RAAB. Translation.

6.  George Norbury MacKenzie, ed.  1907.  Colonial Families of the United States of America.  Grafton Publishers, New York (reprinted 1966 by Genealogical Publishing Co., Baltimore, MD; OCR version online at Ancestry.com).  On pp. 132-137:  a genealogy of Seth Bunker CUPP (b. 1875, PA) giving our subject as his ancestor.  The scholarship in this work is very poor, so I would not accept what it asserts without proof, and I obviously think it is wrong in connecting Seth Bunker to our subject. 

7.  WorldConnect / Ancestry World Trees (online at RootsWeb.com/Ancestry.com).